Tom McTague, chief UK political correspondent for Politico, has tweeted that police officers are walking across Whitehall towards Westminster Bridge with sniffer dogs.
Kirsten Hurrell, 70, was at her newspaper kiosk in Parliament Square when the incident happened.
What I heard myself was a crash. I looked up. I saw this car ploughing into the parliament fence. I thought initially it was some kind of accident. Then I heard a couple of sharp noises. It could have been gunshots. I wasn’t sure.
There was a lot of steam from the car. I thought it might explode. I telephoned the police but someone had already called them. I heard from someone else that the car had mown down people on the bridge.
I saw myself someone lying on the floor near the car. It looked like a cyclist. The car was in the fence.
Hurrell said she fled the scene without locking up her kiosk outside Portcullis House, home to dozens ofMPs.
There was a lot of steam coming out of the car. It looked like steam rather than smoke. I thought it was going to explode.
London Ambulance Service deputy director of operations, Pauline Cranmer, said:
We were called at 2.40pm to Westminster Bridge to reports of an incident, with the first crew arriving within six minutes.
We have sent a number of resources to the scene including ambulance crews, London’s Air Ambulance and our Hazardous Area Response Team.
We are working closely with other members of the emergency services at the scene, with our priority being to ensure patients receive the medical help they need as quickly as possible.
We have declared a major incident and our priority is to assess patients and ensure that they are treated and taken to hospital as soon as possible.
As we are very busy dealing with this incident, we would ask the public to only call us in a genuine emergency.
As news of the attack at Westminster broke, Nicola Sturgeon, Scotland’s first minister hurried from the debating chamber at Holyrood midway through the debate on her new Scottish independence referendum bid.
It is thought Sturgeon may be heading for a meeting of the Scottish government’s security and resilience committee. However, there was no obvious change in the level of policing and security at Holyrood where parliamentary business continued uninterrupted.
Murdo Fraser, the Scottish Tory economy spokesman, raised a point of order during the debate asking whether the sitting should be suspended due to events at Westminster.
Linda Fabiani, the deputy presiding officer, said the Holyrood authorities would not suspend the sitting. “It has been considered and it has been decided to carry on with business as usual,” she told Fraser.
The police says no terrorists have got into the parliament building.
We have been evacuated from Portcullis House to Norman Shaw North, the building next door. MPs have been told to go back to their rooms. We are being told conflicting information about where to go. I’m currently penned in a corridor with hundreds of people.
Owen Bennett, deputy political editor of the Huffington Post, posted an account on Twitter.
He said:
I heard what sounded like an explosion and raised voices outside parliament, and so I rushed to the window.
I saw people running past the entrance to the New Palace Yard entrance to parliament and then at least one person try to run into the Yard itself. A police officer chased this person and wrestled them to ground.
Shots were then fired but I can’t remember how many and I didn’t see who fired them. I ran down the stairs from my office overlooking the Yard to get more information, but the police prevented us from leaving the stairwell.
When I returned to my office, I could see two people lying on the ground outside Westminster Hall, but neither of these were the person I saw wrestled down by the police officer minutes earlier.