A fire at an illegal market in a six-storey building in the eastern Indian city of Kolkata has killed at least 18 people, police say.

West Bengal fire minister Javed Khan said the fire at the Surya Sen market near a railway station in the centre of the city began about 04:00am (22.30GMT) on Wednesday and was likely caused by an electrical short circuit.

Khan said 10 people were admitted to hospital in a critical condition and the death toll was expected to rise.

State fire services director Gopal Bhattacharya said hundreds of firefighters attended the scene and some people died of suffocation in their sleep.

"We found dozens of people lying unconscious with severe burn injuries on the floors of shops," Bhattacharya told AFP news agency.

Police were looking for the owner of the building, which was filled with dozens of small shops selling various plastic products.

A police official, speaking on condition of anonymity because he was not authorised to speak to the media, called the scene of the fire "an illegal, unauthorised market".

Kolkata residents said the market had operated in the building for nearly 40 years. They said there was only one entrance to the building, which made rescue efforts difficult.

The building housed several warehouses on its upper floors, where chemicals, paper and plastics were stored.

Police said the victims were porters working in the market, who also slept there at night.

Source: Agencies