Two people were injured when a car drove into security barriers outside the British parliament on Tuesday and the driver - a man in his 20s - was arrested, emergency services said, with counter-terrorism police leading the investigation into the incident which is being treated as a terrorist incident.

DEVELOPING: A man has been arrested on suspicion of terrorism after driving a car into a gate outside the Houses of Parliament in London, police say https://t.co/7pmx11nQxp pic.twitter.com/dIXlfYlq0t — CBS News (@CBSNews) August 14, 2018

Television pictures from the incident showed armed police surrounding a silver saloon car that had hit heavy barriers outside St. Stephen’s Gate, the main public entrance to Parliament. Its hood was crumpled and its airbags had been deployed. A rooftop camera showed the moment the car crashed into barriers outside Parliament in London.

Rooftop camera shows moment car crashes into barriers outside Parliamenthttps://t.co/CprbiGZgrg #Westminster pic.twitter.com/0noYclQNaR — BBC Breaking News (@BBCBreaking) August 14, 2018

London’s Ambulance Service said it had treated two people for injuries at the scene and they had been taken to hospital. Neither of those hurt were believed to have suffered serious injuries and police said they were trying to piece together what had happened.

London: Parliament Crash Latest: Massive Armed Police Response as Car Crashes Into Westminster Barriers ht pic.twitter.com/tA3UyQpKNO — RJD (@rjddrk) August 14, 2018

"At this stage, we are treating this as a terrorist incident," the Metropolitan Police said in an emailed statement. The driver of the car, a man in his late 20s, was arrested on suspicion of terrorist offenses, the police said.

The Metropolitan Police’s Counter Terrorism Command is investigating an incident in #Westminster this morning during which a number of people were injured. Keep following @metpoliceuk for updates. https://t.co/mcyVXyiOPi — Metropolitan Police (@metpoliceuk) August 14, 2018

“While we are keeping an open mind, the Met’s Counter-Terrorism Command is leading the investigation into the #Westminster incident,” London’s Metropolitan Police said on Twitter.

Earlier, police said the male driver of the car had been arrested at the scene of the crash which occurred at 0637 GMT.

At 0737hrs today, a car was in collision with barriers outside the Houses of Parliament. The male driver of the car was detained by officers at the scene. A number of pedestrians have been injured. Officers remain at the scene. We will issue further info when we have it. — Metropolitan Police (@metpoliceuk) August 14, 2018

Quoted by Reuters, witness Jason Williams said the car had struck a barrier on a lane used for access to the parliament building with force. He said he thought it was deliberate.

“It’s a very serious incident,” he told reporters. “There was smoke coming from the vehicle.”

Images shot by a Euronews journalist showed police pointing their guns at a vehicle. Footage on social media showed a handcuffed man being led away by heavily armed police. Other footage showed a cyclist lying on the street.

“I saw the cyclists, injured cyclists. I’ve seen people, about 10, on the road, lying down, but I haven’t seen any fatalities,” Williams said.

Westminster Underground station, close to parliament, was closed to the public and the building cordoned off.

Parliament is in summer recess and most lawmakers are not using the building. Prime Minister Theresa May is on holiday abroad.

This is the latest attack on high profile London landmarks: in March 2017, Khalid Masood, 52, killed four people on nearby Westminster Bridge before he stabbed to death an unarmed police officer in the grounds of parliament. He was shot dead at the scene. It was the first of five attacks on Britain last year which police blamed on terrorism.

Britain is on its second highest threat level of “severe”, meaning an attack by militants is considered highly likely.

Last week, a Muslim convert admitted plotting to kill more than 100 people by driving a truck into pedestrians on London’s Oxford Street, the capital’s major shopping thoroughfare.

In October last year, 11 people were injured when a car collided with pedestrians near London’s Natural History Museum, raising fears of an attack, but police later said the incident was a road traffic accident.