Panic gripped the passengers as thick smoke was seen coming out of the second compartment of a Dumdum-bound metro rake between Maidan and Rabindra Sadan metro station around 5 p.m. on Thursday.

"We saw a fire on the track outside the rake. The compartment was filled with smoke. The train was moving in that condition. It was like the film Burning Train (a 1980 Bollywood action thriller in which the Super Express catches fire on its inaugural run and continues to move at full speed)," said a passenger.

Senior officials of Kolkata Metro, city police and personnel of West Bengal fire service and the disaster management team rushed to the spot and carried out immediate evacuation of the stranded passengers. The metro authorities have ordered a high-level probe.

"Forty (passengers) were brought to the hospital for treatment. Five of them were admitted in the SSKH Hospital," state public works minister Aroop Biswas said. But an official of the hospital said seven people have been admitted.

Biswas said chief minister Mamata Banerjee, now on tour at Gangasagar in South 24 Parganas district, was monitoring the situation.

"One passenger has a fracture in his leg. Some others are under oxygen support," said city mayor Firhad Hakim.

A Kolkata police officer said all the passengers and staff have been evacuated from the rake.

The metro authority confirmed the fire has been successfully put out and urged people not to panic.

"We disconnected the power supply on the track and the train and stopped the train inside the tunnel as soon as we heard about the smoke. The fire on the outside was put out. Some glass window panes had to be broken to rescue the passengers. We are happy that a major accident could be averted," Kolkata Matro CPRO Indrani Banerjee said.

The official said the metro railway was running a truncated metro service between Noapara and Central and New Garia to Tollygunge.

She said the evacuation was started at 5.20 p.m. and completed by 5.50 p.m.

However, many commuters who were evacuated from the train, complained that they were stranded for more than half-an-hour after the fire broke out while some alleged no announcement was made by the motorman of the train.

They claimed some of the passengers fell ill due to the smoke and alleged that the rescue operation was delayed.

"According to primary investigation, it seems that a spark in the TRCC third rail that supplies power to the trains might have caused the fire. The situation is under control. We are probing the matter," said Jag Mohan, Director General of West Bengal Fire and Emergency Services.

State Fire Services Minister Sujit Bose claimed that the metro railway's alarm system did not function causing panic among the passengers.