Up to 15 people, mostly patients, were feared trapped after part of a hospital roof caved in on Fridayc officials and eyewitnesses said.

Rescuers moved in heavy machinery to cut through the crashed roof of the female surgical ward of Kasturba Hospital, hospital spokesman Vinodanand Jha told AFP.

"Twelve to 15 patients are feared trapped and a relief operation is on," Jha said, adding that rescuers had already dug out five survivors.

Debris showered on the ward's inmates, trapping them after the roof tumbled at around 2:30 pm (0900 GMT), Jha said.

He was unable to say how the accident occurred in the hospital, which is run by the state-owned Bharat Heavy Electricals Ltd. firm.

"Right now, relief operations are our priority and then we will try to find out how the accident happened," he said.

A staffer for the ambulance service said the roof collapsed without any warning and fell "in a shower of debris of bricks and mortar".

"It happened very suddenly," the worker, who did not give his name, told AFP by phone.

Bhopal witnessed the world's worst industrial disaster in 1984 when tonnes of lethal toxic gas leaked from an Union Carbide pesticides plant, killing tens of thousands of city dwellers.

US-based Dow is the parent company of Union Carbide.