At least 73 people have been killed after a fire swept through a hospital in the eastern Indian city of Kolkata, officials have said.

The blaze, which started in the early hours of Friday morning in the basement of the seven-storey AMRI hospital, killed mostly patients, who were trapped by the smoke and flames.

Satyabrata Upadhyay, a senior vice-president of the AMRI hospital company, confirmed 73 people had died, including three hospital workers.

Suggesting that the fire had been sparked by criminally negligent behaviour, Mamata Banerjee, the chief minister of West Bengal, said it was a "serious offence" and that the authorities would "take the strongest action".

As rescuers scrambled to evacuate survivors, police filed a case against the hospital for violating safety procedures.

Authorities believe the fire was triggered by flammable materials such as oxygen cylinders that were stored in the basement.

Sadia Azim, a journalist in Kolkata, said the blaze was a "massive tragedy" for the people and the city.

"It was total chaos [when the fire began]. There was smoke all around," she told Al Jazeera.

Azim said there was was no fire-fighting equipment and that fire alarms did not work.

Moon Chakraborty, who was in the hospital with a broken ankle, called her husband at home to tell him a fire had broken out.

"She had died by the time I reached the hospital," her husband, S Chakraborty, said.

Ahmed Javed Khan, the disaster management minister for West Bengal, told Al Jazeera the toll might increase due to suffocation and asphyxiation. 

Smoke hinders rescue

A fire incident at the same hospital in 2008 caused damage but there were no deaths.

Local television channels showed patients being rolled out on stretchers and distraught relatives waiting outside the hospital as a thick layer of smoke engulfed the seven-storey building.

Two dozen fire trucks were sent to douse the blaze and evacuate the building, but thick smoke hindered rescue operations, officials said.

"The hospital is such that neither the ladders nor the fire brigades could get through ... so the rescue operations got a little delayed and in that time the smoke had risen up to the higher levels," Firhad Hakim, the state's urban development minister, told reporters.

Source: Al Jazeera and agencies