Metro services were disrupted for eight minutes on Tuesday evening because of a mystery man.

A driver of a Dum Dum-bound rake allegedly spotted a man walking down the tracks in the tunnel between Netaji Bhavan and Rabindra Sadan stations and stopped the rake. Metro officials, however, said a search revealed no one.

The driver alerted the control room just after 6.30pm and the staff at Rabindra Sadan station cut off power supply to the tracks before manually checking the tunnel. The train resumed its journey at 6.40pm after the search team said they did not spot any one.

Metro officials denied that any man had entered the tunnel. A Metro spokesperson said the train was delayed by four minutes at Rabindra Sadan station to pick up a passenger.

"The train was not stranded inside the tunnel. It was about to leave Rabindra Sadan when a guard told the driver that a passenger had been unable to board the train. The door was reopened to take the passenger in. This took four minutes," said the spokesperson.

But regular Metro commuters could not recall a single instance of a train driver opening the door because a passenger had been left behind on the platform.

Metro sources said a driver of a Dum Dum-bound train had reported sparks flying from the third rail inside the tunnel between Netaji Bhavan and Rabindra Sadan. The service was held up for around five minutes. Metro officials blamed the sparks on foreign particles coming in contact with the third rail.

In case of such disturbances, Metro employees usually inspect the spot but only after power has been switched off and the control room alerted.

"No such process was followed today. It was unlikely that someone was inspecting the tracks hours after the incident, that too without switching off power. However, the driver clearly said he had seen a man walking on the tracks, around 300 metres away from the Rabindra Sadan platform," said the Metro official.