Politicians described chaotic scenes in Westminster after a security alert meant many had to be evacuated from Parliament.

Peer Sheila Noakes wrote: "Shots in Parliament Square. People running like crazy."

Conservative MP Grant Shapps tweeted: "Police response instant. Heard commotion, looked round. Police weapons drawn, 4 shots, police ordered us to hit ground & get back, get back."

Fellow Tory Michael Fabricant described a similar scene, saying: "I was walking briskly to a vote when crowds of MPs rushed towards me saying that shots have been fired and shouts of 'get back'."

Liberal Democrat leader Tim Farron tweeted shortly after news of the incident broke: "Currently with a shell-shocked group of MPs at New Scotland Yard having been evacuated following the attack. Police doing an incredible job."

Many MPs spoke about being locked inside rooms in the Parliament building. Green Party leader Caroline Lucas tweeted: "Locked in Commons with fellow MPs. Thoughts with innocent people hurt today and thanks as ever to Police & other staff working so hard here."

 Labour's David Lammy wrote: "Locked in the Commons Chamber but my heart goes out to the police officers, those hit by the car on the bridge and their families. Stay safe."

Former education secretary Nicky Morgan told the Press Association: "The Division Bell had just gone and MPs were making their way to the House of Commons chamber. I was walking from Portcullis House along the path of Old Palace Yard when suddenly shots rang out.

"It takes a moment to realise that is actually gunfire and at that point people were yelling get down get back.

"They pushed us all back to the new building.

"We have at the back of our mind all the time that something terrible can happen. The first thing is is that actually gunfire? Have you misheard? But the reaction of the officers around made it very clear this is a very serious situation."

Around half an hour after the attack, former cabinet minister Anna Soubry claimed she and the Security Minister, Ben Wallace MP, were ordered into the Parliament lobby "at gun point" by police officers.

"Colleagues taken out of the library at gun point by counter terrorist armed police officers," she tweeted.

"Armed officers ordered myself and Security Minister into lobby at gun point. Terrifying," she said.