Passengers of the northbound Victoria underground service at Warren Street in London, UK, were evacuated after there was a reported burning smell in the train.
Officers from London Underground and British Transport Police (BTP) moved the passengers to safety last evening.
Investigations into the incident revealed the smoke was caused by ‘mechanical issues’.
A BTP spokesperson said: "Some passengers had reported noticing the smell of burning from the train.
"There is no suggestion whatsoever that the mechanical issues are linked to criminal activity, and the armed officers who attended did so as they were closest to the incident at the time and were able to provide the quickest possible response."
The incident follows a series of arson attacks on the main line between Birmingham and London early Monday morning.
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The trains on the line were delayed by four hours due to a number of fires along the line at Canley, Coventry. The fires were started in the troughing, a concrete channel that houses the signaling cables and runs alongside the tracks.
BTP detective inspector Roger Trimble said: "We’re in the very early stages of an investigation and while it is too soon to say exactly how the fires began, we know they were started deliberately.
"We would like to reassure people that this is believed to be an isolated incident rather than a wider attack on the rail network."
Network Rail has issued a statement that it is working closely with the BTP in the aftermath of the attacks in Paris, France.
"Along with BTP and our industry colleagues, we are monitoring the situation closely and reviewing what has taken place. The safety of the public and rail staff is our utmost priority, and BTP will continue to maintain a security presence on trains and at stations," the statement added.
Image: BTP and Police Community Support officers at a London station. Photo: courtesy of British Transport Police.