Man and woman were hurt in the accident near Watford Junction
A train has hit a landslide in south-east England, causing it to strike another train and derail.
A man and a woman were injured in the accident near Watford Junction, at the Hunton Bridge Tunnel.
Emergency services and engineers are on the scenes and trains in and out of London Euston are facing "major disruption".
The landslip was caused by torrential rains, which have prompted an amber flood warning in the east, south and south-east of the country.
Network Rail said that although a "small portion" of the train came off the track it "remained upright". Another train travelling in the opposite direction gave it a "glancing blow", it added.
"Passengers are being transferred to continue their journeys," a spokesman said.
"Initially, all lines of the West Coast main line at this point were blocked but two of the four lines reopened at about 8am and services have resumed."
Some services have been cancelled and the disruption is expected to last throughout the morning.
"Our priority is to fully reopen the railway as soon as it is safe to do so. A full investigation into what happened will take place," Martin Frobisher, route managing director for Network Rail, said.