Dramatic footage shows crowds of terrified people rushing away from the scene after police reported an incident just after 10:30pm tonight.
Armed police are at the scene and Transport for London confirmed the bridge has been closed in both directions.
Several police vans swooped on the scene after witnesses describe a van mounting the pavement on the bridge, with some police officers describing the scene as a “terror attack”.
Terrified revellers fled the scene after a 'major' incident on London Bridge
Nearby Underground stations Monument and London Bridge were put on lockdown and police dogs were seen patrolling the area.
One witness comforting her distraught friend told Express.co.uk: "We saw a vehicle mow down like five or six people."
Three people were also seen with what appeared to be knife wounds, according to Reuters news agency.
Some witnesses also told Sky News they heard gunfire at the scene.
London Bridge has been closed by armed police
Shaken witnesses on Twitter describe the event as “Westminster bridge all over again”.
The attack comes just weeks after crazed Khalid Masood ran over pedestrians on the bridge before stabbing a police officer, killing five.
Get Quotes on Home Insurance