Passengers were evacuated from a bus today after a man on board pulled out a suspected gun, police sources said.
Scotland Yard firearms officers were seen handcuffing a middle-aged man after the number 73 "bendy bus" was forced to stop near Victoria railway station in central London.
One man - believed to be in his 50s - was taken away for questioning.
Parts of Terminus Place were blocked off after passengers were ushered to safety shortly after 1pm.
One onlooker, who did not want to be named, said: "There was a rush of sirens and a lot of confusion. At first everyone thought it was some sort of terror incident.
"Whenever you see a van full of firearms officers, you assume it is something serious."
The suspect was bundled into the back of a police van to be questioned.
Another man, who saw the suspect being taken away by officers at the busy station, added: "He appeared to be drunk - he was stumbling."
Scotland Yard confirmed no one was hurt in the incident.
Witnesses who saw the scene unfold at Victoria posted messages on blogging website Twitter.
Simon Duke wrote: "Whole of Victoria station shut off, guy with gun on bus outside. Armed cops taking up position now with riot gear on."
Kate Lavender, from Brighton, later added: "Victoria station closed earlier - then a gunman arrested and life resumes with barely a break in stride - hey ho."Reuse content