A tube station in London around Old Street station was reopened late Saturday night after reports of a bang led to it being evacuated by armed police, the Telegraph reports.

The scene was chaotic as more than 20 ambulance and dozens of armed police stormed the scene and evacuated the station.

Stay away from Old Street, reported incident inside station. pic.twitter.com/2SY0aGNkd3

— Sam Hanover (@Sam_Hanover) September 30, 2017

Police vans surrounding old street station, including unmarked vans now. Armed officers everywhere pic.twitter.com/0rGdu2u1Zu

— George Maier (@GeorgeMaier) September 30, 2017

The terror threat level in the UK was raised from "severe" to "critical" in mid-September following an explosion earlier on one of the city's Underground trains.

"Police were called at approximately 21.20pm on Saturday to reports of a man believed to be acting suspiciously on an underground train,” said a spokesperson for Scotland Yard.

"Several people subsequently reported hearing a bang. No firearm or any other object was seen. Officers, including firearms officers and the British Transport Police, attended the Old Street area and the station was temporarily evacuated. There were no reported injuries. At this stage nothing suspicious has been found and the incident has now been stood down."