Indian-origin lawmaker Keith Vaz was among those inside the building along with 400-odd members. "We are all locked in the chamber in the House of Commons, there are 400-odd MPs here and we cannot leave," Mr Vaz told NDTV. Mr Vaz, 59, said members heard gunshots. "We have been told that the attacker was shot. An air ambulance has arrived and everything is in a lockdown situation. This is all very alarming. We do not know what is happening."
The attacks come a day after UK, following the US, banned passengers traveling from airports in several middle-eastern airports from bringing laptops, tablets and other portable electronic devices on board with them when they fly.
Here are latest updates on attack near UK Parliament:
President Pranab Mukherjee and Prime Minister Narendra Modi expressed sadness over the terror attack on the UK Parliament on Wednesday, where five people - including the perpetrator - were killed and dozens were severely injured.
India stands by UK ; terrorism must be met through collective action by international community- President of India (@RashtrapatiBhvn) March 23, 2017
Shocked to hear of terrorist attack in London ; condolences to bereaved families & prayers for recovery of injured # PresidentMukherjee- President of India (@RashtrapatiBhvn) March 23, 2017
The US president's oldest child took aim at Sadiq Khan, the mayor of London, who was quoted last year by the Independent, a London newspaper, saying terrorism preparedness had to become part of the fabric of major cities.
World leaders unanimously condemned the attack in the heart of London by a man who was shot dead by armed police, with many saying they stand with Britain.
Deeply saddened by the terror attack in London. Our thoughts and prayers are with the victims and their families.- Narendra Modi (@narendramodi) March 23, 2017
In Brussels to commemorate the one-year anniversary of attacks on the main airport and a metro station, Juncker said "the fact that exactly on the same day something similar happened in London, and to London, is really putting me in the situation of someone who does not have...enough words to express how I am deeply feeling."
"I heard a thud, turned round and there was a man lying about 10 yards away from me," Reuters photographer Toby Melville recalls, describing the moment a man fell from London's Westminster Bridge to the pavement below
"Islamist-related terrorism is our assumption," top counter terrorism officer Mark Rowley told journalists. The male assailant was shot dead after mowing down pedestrians and stabbing a policeman.
A/Dep Cmsr Rowley: "At this stage - but it may change - we believe approx 40 people were injured including three police officers."- Metropolitan Police (@metpoliceuk) March 22, 2017
A/Dep Cmsr Rowley: "It is an incredibly sad & sombre day & only right I mention the pride I feel in our officers' swift & brave response."- Metropolitan Police (@metpoliceuk) March 22, 2017
A/Dep Cmsr Rowley: "Three members of the public also lost their lives in this attack. Specially trained officers will support them."- Metropolitan Police (@metpoliceuk) March 22, 2017
Canada has tightened security, especially on Parliament Hill, after the deadly attack outside parliament in London, an official said.
Merkel said Germany stood by Britain "firmly and resolutely".
"Although the background to these acts are not yet clear, I reaffirm that Germany and its citizens stand firmly and resolutely alongside Britons in the struggle against all forms of terrorism," Merkel said in a statement.
"In these grave moments, we Germans feel very close to the British people," President Frank-Walter Steinmeier added.
Theresa May's thoughts are with those killed and injured in an attack close to parliament and the British prime minister is being kept updated with developments, her office said on Wednesday.
New York police ramped up security at British sites across the city, reports news agency Reuters.
BREAKING: London police say they believe there was only one attacker.- The Associated Press (@AP) March 22, 2017
India strongly condemns Westminster terrorist incident & condoles loss of life. No place in democracies & civilised societies for terrorism.- Gopal Baglay (@MEAIndia) March 22, 2017
Police are still searching for one of the two people believed to have launched Wednesday's attack outside the British parliament building, Daily Telegraph newspaper reported.
A woman has been pulled from the River Thames alive after Wednesday's attack on a bridge near Britain's parliament in Westminster, the Port of London Authority (PLA) said, adding that she was being treated for serious injuries.
MPs who were locked inside parliament after the parliament attack have been allowed to leave. According to reports there were 400 lawmakers inside the parliament when the incident took place.
We are inside a sealed chamber in UK Parliament. 400-odd MPs here and we can't leave: UK lawmaker Keith Vaz to NDTV on Westminster incident pic.twitter.com/U7N1pUXEG9- NDTV (@ndtv) March 22, 2017
US President Donald Trump told reporters at the White House he had been briefed on events in London but gave no details
One woman has died and other people are being treated for "catastrophic" injuries after an attack near parliament on Wednesday, British news agency Press Association reported, citing a junior doctor at a central London hospital.