Police have defused a bomb found in a car parked in London's West End.
Explosives officers were called to The Haymarket, in the heart of theatreland and close to Regent Street's popular shopping area, following reports of a suspicious vehicle left there.
They discovered a "potentially viable explosive device" which they made safe.
The area, including Piccadilly Underground station, has been cordoned off and will remain closed for most of the morning, police said.
A terrorism investigation has been launched.
Contrary to rumor, the bomb in question was not the new stage production of The Lord of the Rings: The Musical.
The BBC has more:
One police source said the bomb was a "big device" and posed a real and substantial threat to the area around The Haymarket, which is in London's theatreland.
A witness reported seeing gas canisters being removed from the car, believed to be a silver Mercedes, at around 0400 BST (O300 GMT).
Bouncers from a nearby nightclub said they saw the car being driven erratically before it crashed into a bin. They said the driver then got out and ran off.
The authorities are taking this very seriously and it's disrupting life in London:
Police say The Haymarket is likely to remain closed for some time and severe travel disruption is predicted.
Piccadilly Circus Tube station is closed and trains are not stopping, while local bus services are being diverted.
The BBC's Daniela Relph, at the scene, said the heart of London was completely closed off and police officers were concentrating on keeping people away.
Thousands of commuters have been unable to get to work.