Officers from British transport police have evacuated a train and searched a number of passengers following reports that a man was seen carrying a weapon.
Police were called to London Bridge at around 3pm on Friday.
Platforms five and six were closed to the public following the security scare and part of the platform was cordoned off.
The 1.58pm Thameslink service from Rainham to Luton was delayed by 18 minutes after officers cleared the train and carried out a number of searches of passengers.
Following the search the train was allied to continue on it advertised route.
BTP have been approached for comment