London Bridge railway and underground stations were closed off and evacuated due to an abandoned and smashed up VW Polo.
The entire area was off limits for around an hour from 1.40pm, leaving hundreds of people crowded at the police cordon, because the vehicle was deemed "suspicious" by the Metropolitan Police Service.
An eyewitness described how a bomb disposal robot was deployed and a Met Police officer later confirmed nothing suspicious was found.
Southern Rail said trains at London Bridge had to sit in situ, and incoming trains terminated at New Cross Gate, Norwood Junction, East Croydon and Bermondsey.
Jubilee and Northern Line tube trains were running as normal but not stopping at the busy Thames-side station.
A journalist at The Times, which has offices in the News UK building opposite the station, claimed police said it was down to a stolen vehicle abandoned in a taxi rank.
Witness Felix Meller described how hundreds were evacuated from the station, some running out in confusion, and how hundreds were still crowding around the cordon and spilling onto the road.
The 34-year-old said he was crossing London Bridge from The Monument, when the road was closed off to traffic, before he was evacuated while trying to use a nearby gym.
"I then went into the station but a minute after that the whole station was evacuated," said the recruitment firm owner.
"One woman started running and everyone then followed. It was a nerve-wracking moment because you don't know what's going on. It's herd mentality.
"One or two security staff were then shouting from inside the station."
He added: "There are now hundreds of people watching and hanging around. Everyone in the News UK building appears to have been evacuated but I can still see some people in the Shard.
"Everyone is streaming out of the station now, but police officers are asking people to clear away from the top concourse between the Shard and the station."
Mr Meller said he saw what appeared to be a robotic bomb disposal unit being driven from the station towards a police vehicle at around 3.15pm.
A Met Police spokesman said: "After checking it out we found it was no longer suspicious."