A Tube train has derailed at Hammersmith station, but there are no reported injuries.
London Underground has launched an investigation
All the carriages of the Piccadilly line train remained upright, according to British Transport Police (BTP).
It is believed the wheels of the rear carriage came off the track at 2125 BST on a broken rail as the train carrying 76 people was travelling between Hammersmith and Baron's Court stations.
A BTP spokesman said there was no suggestion of any crime and an investigation was under way to establish the cause.
Around 20 metres of track and signal equipment in the area will have to be repaired overnight.
According to sources at the crash site the incident was caused by a broken rail, and a member of the rail staff who saw the rail said it was "rusted" before it fractured.
It is the second Tube derailment this year, following one at Chancery Lane in January, which injured 32 people.
Passengers walked to safety though the carriages and to another train which was
brought into position in front of the affected train.
Firefighters, British Transport Police and Underground staff were on the second train to help passengers.
A London Underground spokesman: "There was a very low speed derailment on a
Piccadilly Line train.
"There were no reported injuries. As far as we understand at this time only
the last wheels on the last carriage came off.
"We don't know the cause of the derailment. There will be a full
The spokesman said there would be disruptions to the service but was unable to
confirm how long they could last.
Services are suspended between Acton Town Station and Hyde Park Corner Station in both directions.
A Scotland Yard spokeswoman said there were no other trains involved in the incident, which occurred 200 yards from Barons Court station, she said.
London Fire Brigade said four fire engines were sent to Hammersmith and one to
The Central Line was suspended for months after the Chancery Lane incident, causing mounting frustration for passengers.
An independent inquiry team found it crashed after a traction motor beneath the train fell off and hit the track.