Northern Ireland MPs have been caught up in the "terrorist incident" at Westminster.
A policeman has been stabbed and his attacker shot by officers after a major terrorist incident at the Houses of Parliament.
The attacker mowed down several pedestrians as he drove a grey Hyundai i40 across Westminster Bridge before crashing it into railings then running through the gates of the Palace of Westminster and stabbing the officer.
Eyewitnesses said he was shot by police as he approached a second officer clutching his knife.
London police are treating it as terrorist "until we know otherwise".
Speaking from inside Westminster, Fermanagh & South Tyrone MP Mr Elliott said: "Westminster has been shocked by today’s events in which a number of people were mown down by a vehicle on Westminster Bridge and a knifeman later entered Old Palace Yard and attacked a police officer.
“These incidents are obviously very concerning indeed, coming as they do on the first anniversary of the Brussels terror attacks.”
South Antrim MP Mr Kinahan said: “Today’s attack is a reminder of the threat which is faced by all democratic societies. I understand a Police officer has been injured by an attacker with a knife. This is a reminder of the debt of gratitude we owe to the Police and the security services who risk their lives every day to protect us all.
“My thoughts are with all those who have been injured.”
Northern Ireland MP Jeffrey Donaldson tweeted: "Walking into Parliament when attack occurred. Police excellent. Got us onto ground then led to safety. Terrorism will never defeat democracy."
Immediately before the incident, at around 2.45pm, a crowd of passers-by was seen running from the direction of Westminster Bridge and around the corner into Parliament Square.
Press Association reporter Laura Harding, who was in Westminster at the time of the incident, said: "Everyone has been evacuated into Central Lobby, including a group of schoolchildren and kitchen staff - around 15 schoolchildren aged around 10 - with armed police coming through the lobby now.
"The children are really calm, the teachers are comforting them.
"Everyone is standing around on their phones.
"There are also a bunch of young people from the Hammersmith Boxing Club in their tracksuits and the British Lionhearts boxing group."
Commons Leader David Lidington told MPs: "What I am able to say to the House is there has been a serious incident within the estate.
"It seems that a police officer has been stabbed, that the alleged assailant was shot by armed police.
"An air ambulance is currently attending the scene to remove the casualties.
"There are also reports of further violent incidents in the vicinity of the Palace of Westminster but I hope colleagues on all sides will appreciate that it'd be wrong of me to go into further details until we have confirmation from the police and from the House security authorities about what is going on."
Prime Minister Theresa May was seen being ushered into a silver Jaguar car as what sounded like gunfire rang out at Parliament during the incident.
Politicians have described scenes in the Commons as "chaotic".