Passengers had to be evacuated from a train after it derailed while leaving Paddington station in London.
The rear power car of the Great Western Railway train partially left the track as it departed for Penzance in Cornwall shortly before midday.
A spokesperson for the rail firm said it was "travelling at extremely low speed" and no injuries were reported.
Platforms one and two are currently out of use while Network Rail investigates what happened.
The passengers on board were transferred to another service and other trains leaving the station are running to their original timetables.
It is the second time a train has derailed at a major London station in a week.
On Tuesday, a South West train left tracks after it hit a barrier train at Waterloo station causing major disruption for commuters.
On the same day, a Great Northern train crashed into buffers as it arrived at King's Cross.