A fire has killed more than 60 people at a private hospital in the eastern Indian city of Kolkata.

Authorities say the blaze swept through the AMRI Hospital early Friday in the capital of West Bengal state.

Local television channels showed patients being rolled out on stretchers and distraught relatives waiting outside the hospital as smoke engulfed the multi-story building.

Rescuers broke windows to get to some of the patients who were trapped and later moved to a nearby hospital.

West Bengal Chief Minister Mamata Banerjee promised a full investigation into the incident, after government officials alleged that some hospital staff fled the scene when the fire broke out.

Banerjee also said action would be taken if fire prevention standards were found to be below-standard.

Some 160 patients were said to be in the hospital at the time of the blaze.

Firefighters worked to bring the blaze under control and rescue those still trapped inside the building, after maneuvering narrow surrounding streets to reach the Kolkata hospital.

Officials say the fire broke out in the hospital's basement, where chemicals were stored.