Video footage shows a man pouring a liquid onto a road and lighting it on fire moments after a car crashed into a north London police station.
Scotland Yard said Edmonton Police Station on Fore Street was evacuated after the vehicle struck the building shortly before 7pm on Wednesday.
The Metropolitan Police later confirmed a man in his 40s had been arrested on suspicion of arson and other offences in connection with the incident.
Counter-terrorism officers are also supporting the investigation, the force confirmed.
Footage posted online shows a man leaving the car and pouring a substance onto the road from a container, as onlookers watch on in horror.
Standing in front of a double-decker bus, he then sets the liquid on fire.
Witnesses can be heard shouting as a police car pulls up and officers run out to tackle the man at a bus stop metres away.
Another police officer appears to use a fire extinguisher to put out the flames on the road.
Store manager Ogur Mazlum, 34, works nearby and witnessed the moment the car crashed into the police station.
Speaking on behalf of Mr Mazlum, who speaks limited English, his wife Serife Mazlum, 32, told the PA news agency: “He literally just walked out (of his shop) to just call me and see if everything’s OK at home.
“Then he said I have to shut the phone quickly.
“That was when the car crashed into the front of the police station.”
Mrs Mazlum said her husband saw that the car had crashed through a glass entrance to the police station and that a man was unable to enter through a second barrier despite attempts.
“He was insisting on trying to get inside, but the glass door wouldn’t break anymore so he couldn’t get any closer,” she added.
“Then he casually got out of the car with a tank of petrol. He poured it down from the car into the middle of the road and then he just set it on fire.”
Mrs Mazlum added that “luckily” the man had “missed a spot” and the flaming petrol did not reach traffic which had stopped on the road nearby.
She said another man watching the scene from across the street ran to intervene after the driver had set the fuel alight.
“He pinned (the driver) to the ground just as the police were arriving,” she said.
“So by the time the police came and got out of the cars, the citizen had already slammed him to the ground.”
She said efforts were then focused on extinguishing the fire, which was “just getting worse”.
The Met said the vehicle had been examined by specialist officers.
No injuries were reported and officers returned to the station at about 10pm.
A large cordon around the scene has also been reduced in size, the Met added.