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.
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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