Missing Malaysian Airlines MH370 crashed into the southern Indian Ocean according to flight data, the Malaysian Prime Minister has said.
Najib Razak held a news conference on the latest developments this afternoon.
He said flight data had shown the aircraft was last recorded in the middle of the southern Indian Ocean.
Malaysia Airlines officials have told the families of passengers from missing flight MH370 to assume "beyond doubt" that no one survived.
The airline said in a text message to family members that "we must now accept all evidence suggests the plane went down in the Southern Indian Ocean".
Speaking at a press conference in Malaysia today, prime minister Najib Razak said: "Based on new analysis we have concluded [the jet] flew along southern corridor and that its last position was in the middle of Indian Ocean west of Perth.
"This is a remote location far from any possible landing site.
"It is therefore with deep sadness and regret that I must inform that in accordance with this new dqayta Flight MH370 ended in the southern Indian Ocean."
Moments earlier, officials from Malaysia Airlines sent an SMS text message to the families of the passengers on board when the plane was lost which said "we must now accept all evidence suggests the plane went down in the Southern Indian Ocean".
"Malaysia Airlines deeply regrets that we have to assume beyond any reasonable doubt that MH370 has been lost and that none of those on board survived," the message read.
Mr Razak said he had been briefed by representatives from the UK Air Accident Investigation Branch (AAIB), which informed him that satellite data from the UK company Inmarsat, using techniques "never before used in an investigation of this sort", revealed the final position of the plane.
"Malaysia Airlines has already spoken to the family of the passengers and crew to inform them of this development," Mr Razak said.
"For them the past few weeks have been heartbreaking. I know this news must be hard as well."
The Malaysian prime minister made no reference to debris found in the southern Indian Ocean over the course of the day, with several white and orange objects spotted in the search area now identified as the region where the jet came down.
Earlier, the Malaysia transport minister, Hishammuddin Hussein, said that an Australian naval ship could locate possible debris within hours.
The Australian Maritime Safety Authority (Amsa) confirmed that the HMAS Success had made its way out to the remote search area some 2,500km (1,550 miles) from Perth, and that the objects were seen within the stretch of water being scoured today.
"HMAS Success is on scene and is attempting to locate and recover these objects," Australian Prime Minister Tony Abbott said in a statement to parliament.
So far, ships in the search effort have been unable to locate several "suspicious" objects spotted by satellites in grainy images or by fast-flying aircraft over a vast search area in the remote southern Indian Ocean.
Earlier on Monday spotters on a Chinese plane said they had seen two white, square-shaped objects in the southern Indian Ocean, at that stage the second possible sighting of plane debris made with the naked eye in the search for the missing Malaysia Airlines Boeing 777.
Spotters aboard that search plane reported the coordinates to a Chinese icebreaker ship, Xue Long, which was making its way to the area - as well as to the central Australian command centre.
In addition to the two larger floating objects, the searchers also reported seeing a range of smaller, white debris scattered over several square miles, according to China's Xinhua news agency.
The sightings were all made in the area identified in previous satellite images from Australia and China.
The developments came as the US prepared to send a specialised device that can locate black boxes into the region.
The US Pacific command said the Towed Pinger Locator, which is pulled behind a vessel at slow speeds, has highly sensitive listening capability so that if the wreck site is located, it can hear the black box pinger down to a depth of about 20,000 feet.
Commander Chris Budde, a US Seventh Fleet operations officer, said: "This movement is simply a prudent effort to preposition equipment and trained personnel closer to the search area so that if debris is found we will be able to respond as quickly as possible since the battery life of the black box's pinger is limited."
The two Chinese planes joining the search today increased the number of aircraft to 10 from eight a day earlier.
An Australian plane scouring the search area spotted a wooden pallet and other objects late on Saturday, including what looked like variously coloured straps or belts. However, it was unable to get up close or take photographs, and other aircraft dispatched to the site on Sunday could only see seaweed.
Mystery of plane's crash unsolved
While families of those aboard missing Malaysia Airlines flight MH370 have been given the heartbreaking news that it crashed, the cause of the aircraft's fate remains a mystery.
New data may have been able to confirm that the flight ended in the Southern Indian Ocean, but what led to its demise and that of the 239 people aboard is still yet to be discovered.
Since the plane went missing, experts have speculated on various theories - from a terror attack or highjacking, to pilot error or mechanical problems.
Owen Geach, commercial director of the International Bureau of Aviation, said he had originally given four theories - adverse weather conditions; catastrophic mechanical or electrical failure of the aircraft; an explosion or terror attack mid-air; or the plane had been forced to land, again by terrorists.
He said since then, pilot suicide had also been suggested as a possible cause, and said that although a forced landing could not be ruled out in the light of today's information, it remains unknown what caused the flight to crash.
He said: "We can now rule out the forced to land theory but that still leaves the other three and ... the possibility of pilot suicide has been suggested.
"The search teams will now need to quickly try to locate the black boxes which will give the best chance of determining probable cause."
In the early days of the flight going missing, speculation surrounded a possible terror attack as police revealed one of the passengers had used a stolen passport.
Malaysian police chief Tan Sri Khalid Tan Sri said one of the passengers using a stolen passport on the missing plane was an Iranian asylum seeker who was not believed to be a member of a terrorist group, and it was thought the 19-year-old was planning to reach Germany.
The stolen passports belonged to Christian Kozel of Austria and Luigi Maraldi of Italy and were entered into Interpol's database after they were taken in Thailand in 2012 and 2013.
Police said a travel agent in the Thai beach resort of Pattaya was contacted by an Iranian man known only as Mr Ali to book one-way tickets for the flight with those names.
The Malaysia Airlines plane did not make a distress call - with one possibly explanation that it was blown up by a suicide bomber or a deadly device planted in luggage.
Hijacking was also a possibility, with the disappearance of the Malaysia Airlines plane possibly explained by passengers storming the cockpit as happened on board United Flight 93 during the September 11 attacks in the United States.
Malaysia's air force chief, Rodzali Daud, has said radar indicated that the plane may have turned back, which could suggest engine failure or an electrical malfunction.
Another theory is human error, although the 53-year-old pilot, Zaharie Ahmad Shah, has more than 18,000 flying hours and has been flying for the airline since 1981, while the first officer, 27-year-old Fariq Hamid, has about 2,800 hours of experience and has flown for the airline since 2007.
And while a catastrophic failure of the aircraft is another possibility, the Boeing 777 has a good safety record, while Malaysia Airlines has an excellent safety record as well.
Timeline of missing flight
March 8 - Malaysian Airlines flight MH370 takes off from Kuala Lumpur at 12.41am local time bound for Beijing carrying 227 passengers and 12 crew.
Someone, apparently the co-pilot, makes the final voice communication from the cockpit at 01.19am, saying "All right, good night" to air traffic controllers.
The plane is last seen on military radar at 02.14am heading west over the Strait of Malacca. Half an hour later the airline reveals to the public it has lost contact with the plane. The plane was due to land around 6.30am.
Officials reveal two passports used to board the flight were stolen, raising the first suspicions of terrorist involvement.
March 9 - Malaysia's air force chief says that military radar indicated the missing Boeing 777 jet may have turned back.
March 10 - Vietnamese aircraft search for a plane door spotted in their waters but find nothing.
March 11 - The hunt is widened to cover a 115-nautical mile radius involving 34 aircraft and 40 ships from several countries.
The Malaysian military claims it has radar evidence showing that the missing plane changed course and made it to the Malacca Strait which is hundreds of miles away from the last location reported by civilian authorities. The aircraft was believed to be flying low.
The two male passengers travelling with stolen passports were Iranians who had bought tickets to Europe and were probably not terrorists, Malaysian police said.
March 12 - Satellite images on a Chinese government website shows suspected debris from the missing plane floating off the southern tip of Vietnam, China's Xinhua News Agency says.
The report includes co-ordinates of a location in the sea off the southern tip of Vietnam and east of Malaysia, near the plane's original flight path.
March 13 - Malaysian authorities expand their search for the missing jet into the Andaman Sea and beyond after acknowledging it could have flown for several more hours after its last contact with the ground.
Nothing was found when planes were sent to search an area off southern Vietnam identified by Chinese satellite images. The Chinese Embassy notifies the Malaysian government that the images were released by mistake and did not show any debris from the missing flight.
March 15 - Prime Minister Najib Razak's says the missing airliner was deliberately diverted and continued flying for more than six hours after losing contact with the ground. The plane could have gone as far north west as Kazakhstan or into the Indian Ocean's southern reaches.
Malaysian police have already said they are looking at the psychological state, family life and connections of pilot Zaharie Ahmad Shah, 53, and co-pilot Fariq Abdul Hamid, 27. Both have been described as respectable, community-minded men.
March 16 - The search area now includes 11 countries the plane might have flown over. The number of countries involved in the operation had increased from 14 to 25.
Malaysian defence minister Hishammuddin Hussein said he had asked governments to hand over sensitive radar and satellite data to try to help get a better idea of the plane's final movements.
March 17 - Officials release a new timeline suggesting the final voice transmission from the cockpit of the missing Malaysian plane may have occurred before any of its communications systems were disabled.
Investigators have not ruled out hijacking, sabotage, or pilot suicide, and they are checking the backgrounds of the 227 passengers and 12 crew members, as well as the ground crew, to see if links to terrorists, personal problems or psychological issues could be factors.
March 18 - Ten days after a Malaysian jetliner disappeared, Thailand's military said it saw radar blips that might have been from the missing plane but did not report it "because we did not pay attention to it".
March 19 - Distressed relatives of the missing passengers threaten to go on hunger strike over the lack of information about the investigation.
March 20 - Two objects which could be connected to the missing jet are detected in the southern India Ocean, the Australian prime minister Tony Abbott said.
March 24 - Malaysian Prime Minister tells media the plane crashed into the southern Indian Ocean according to flight data.