Police have detained a man on Parliament Square in Westminster after he reportedly doused himself with what seems to be a flammable liquid.
He was arrested at around 10.44am, the Metropolitan Police Service said on Twitter. He was sprayed with a fire extinguisher.
The man was carrying a lighter and was detained under the Mental Health Act. He has been taken to a central London hospital.
Pictures from the scene show a police officer covering a man in a red coat with foam. Armed police can be seen on the scene, warning bystanders.
No one has been injured, police said.
Conservative MP Huw Merriman, who was at the gate said paid tribute to police.
“Man next to me at Parliament’s carriage gates appears to have poured (what smells like) petrol on himself. Incredibly brave response from police, who are now helping him,” he said.
Transport for London, TfL said that the eastern side of the square had been blocked to southbound traffic.
“Traffic is slow on approach, compounded by multiple closures in the area,” it said on Twitter.
Footage from the BBC showed ambulances outside the gates to New Palace Yard, and a firefighter using a hose to wash the pavement.
A small area around the gates, spilling out into the road appears to have been cordoned off.
There have been several incidents outside Parliament in the last year, including in December when a man was tasered then taken away by police. Earlier this year a civil servant was stabbed in the Home Office.
Meanwhile, data out in July showed that the number of crimes committed in Parliament increased sharply by 50 per cent. These include a steep rise in threatening letters sent to MPs.