Six hundred passengers were evacuated from a rush hour Tube train after it hit a landslide.
The driver of a train "made contact" with several tonnes of earth shortly after leaving Boston Manor station in west London.
He was forced to make an emergency stop but no passengers were injured and the train was not derailed, Transport for London said.
The Piccadilly line between Northfields and Heathrow has been suspended while engineers assess the landslide.
A Transport for London spokeswoman said it was not yet known whether the line would be reopened by this morning. The landslide occurred at about 6.20pm.
She said: "London Underground is currently assessing the impact of an embankment landslip between Boston Manor and Northfields.
"Initial indications are that three to four tonnes of debris has ended up on the track.
"An eastbound Piccadilly line train came into contact with the debris at Boston Manor station.
"600 passengers were successfully detrained within 15 minutes to the platform at Boston Manor.
"There were no injuries."