Euston Station has been evacuated by police after an e-cigarette is believed to have caused "a small contained explosion".
Network Rail told the Independent the station was evacuated due to "a security alert" just before 8pm.
The British Transport Police (BTP) said "an electrical item is believed to have caused a small contained explosion".
It later added an e-cigarette in a bag is likely to have been the cause of the explosion.
No-one was injured and officers from the BTP and search dogs checked the scene to ensure the area was safe.
Network Rail said the station reopened but significant delays are expected on the service because of the incident.
Witnesses said passengers were seen running out of the station in panic.
Bystanders claimed to have seen smoke coming from an item of luggage on the main station concourse.
Rachel Skytta posted a picture on Twitter saying she was "stuck on a train" outside the station because of an "emergency situation"