A woman died and two men were seriously injured after jumping from a second floor flat to escape a fire, police have said.
Another person, believed to be a man, was discovered dead inside the home in Hounslow, west London, during a search by firefighters.
The woman, aged 44, was found outside the building and pronounced dead at the scene shortly after 2.30am on Wednesday morning.
Stuart Wells, 34, saw three people battling to escape the fire. He told the London Evening Standard: "Three people were screaming at the window. They were trying to break the window with a chair. There were flames and I could see their faces. It was horrific.
"The woman flung herself out of the window and crashed into a telephone box head first. It happened so quickly there was nothing anyone could do."
Amrita Singh, 32, who lives in one of the neighbouring flats, told the newspaper: "We heard horrible screaming, 'Help me, help me'. It was so horrible, we are all stunned by this. The explosion was huge."
Other eyewitnesses described how local residents brought out a mattress in a bid to cushion the landing of those jumping.
The two injured men, aged 18 and 37, were taken to St Mary's Hospital, central London. The 18-year-old was later transferred to a west London hospital. They are both in a serious condition but their injuries are not believed to be life threatening.
A Metropolitan Police spokesman said: "The cause of the fire is currently being investigated - at this stage it is being treated as unexplained."
The blaze in New Heston Road was reported by police officers who spotted it while patrolling the area at 1.40am. Eight fire engines and around 58 firefighters were involved in extinguishing the blaze, the London Fire Brigade said. Police believe it started in a second floor flat before spreading to neighbouring properties.