Paddington station has been evacuated due to a fire alert on Saturday and commuters have been warned to expect delays.
Passengers were told to leave the station at about 9.15am when a fire alarm was triggered.
Trains were being held on platforms while firefighters attended the scene.
There have been no reports of injuries.
A spokesman for Great Western Railway tweeted: "Due to fire alarms being triggered at Paddington trains are at a stand still and passengers are being evacuated. Updates to follow."
The spokesman later said trains were now moving, but commuters should expect delays.
Trains are now on the move to and from Paddington but some delays still likely as a result of the earlier fire alarm sounding.— GWR Help (@GWRHelp) November 28, 2015