"I heard some noise and someone screamed", she said.
The silver vehicle can be seen coming along the road next to Parliament Square before moving to turn right towards Westminster Abbey in footage of the incident aired on BBC News.
Eye-witnesses claim the silver auto was driven "at speed" by the man and may have hit pedestrians or cyclists before hitting the security barriers.
Barry Williams, a BBC staff member based at Millbank, said the vehicle drove onto the wrong side of the road and "ploughed" into cyclists waiting at the lights.
London police say that a auto has crashed into barriers outside the Houses of Parliament and that there are a number of injured. "There was a loud bang from the collision and a bit of smoke", Ewelina Ochab told the AP.
"It was a woman, they were clearly quite injured, they weren't moving and they were in the recovery position".
Jason Williams, 45, from Kennington, was walking to work when he saw the crash.
"I think it looked intentional - the auto drove at speed and toward the barriers".
"I don't know whether he meant to hit the cyclist, they may just have been in the way, but he accelerated hard towards the barrier", Williams told the BBC.
"It looked deliberate. It didn't look like an accident", he told AP.
Police officers stand on duty at a cordon near to the Houses of Parliament following an incident where a auto crashed into barriers in central London on August 14, 2018.
"I saw a auto going at high speed towards Parliament".
He said: "I was coming up to Westminster on a Santander bike".
"We're still trying to piece it together", a spokesman said. It appeared to be one of these barriers that the vehicle crashed into on Tuesday.
"I think it's not a regular traffic accident, because there's a barrier there".
"The male driver of the vehicle was arrested by officers at the scene".
Westminster Underground station, close to parliament, was closed to the public and the building cordoned off.
The cordon has been widened twice and sniffer dogs have been seen in the area.
Police in the United Kingdom have arrested a man who crashed a auto into barriers next to Parliament in an incident that British police said they are investigating as a terror attack.
Scotland Yard said a man has been arrested after the incident shortly after 7.30am.
What action have the police taken?No one else was in the auto, which was being searched at the scene. He was alone in the vehicle and no weapons were recovered at the scene.
He said: "Westminster has the most armed police officers of anywhere in the country and you would expect a quick response but the officers seem to have dealt with it very well".