Kolkata, July 20 (IANS): A fire broke out on the fourth floor of a multi-storeyed office building here on Thursday, a West Bengal minister said.

There were no immediate reports of any casualty in the building housing the Gas Authority of India Limited (GAIL) office located on Pretoria Street, state Fire Services Minister Sovan Chatterjee said.

"The fire is now under control. Up to 12 people who were trapped inside were rescued by the police and disaster management teams. Eight are hospitalised," said Chatterjee, who is also the city's mayor.

A school in the vicinity was closed soon after the fire broke out.

"The incident occurred at around 12.50 p.m. Initially, entering the building was difficult as it has a lot of glass walls for which the smoke could not come out. The fire fighters broke the glass walls. There is no more smoke," said the minister.

The cause of the fire is yet to be ascertained.

"It is not certain what might have caused the blaze. Our officials are checking if anyone is still trapped in the office," a fire official said.