Passengers arriving at Britain's Liverpool airport were being kept on their planes on Tuesday after a security alert which a spokesperson described as a "police incident" the local Liverpool Echo newspaper reported.
Britain is on high alert after a series of terror attacks in London and Manchester this year that have killed 36 people.
At Euston, one of London's busiest train stations, people were seen on clips on social media running out of the building.
"Officers are currently at Euston station responding to a security alert," the British Transport Police said in a statement.
"We are investigating but there appears to have been a small contained explosion which is believed to have been caused by an e-cigarette which was in a bag at the station. No one is believed to have been injured."
It said the station should open shortly but there may be delays after officers with search dogs checked that the area was safe.