Boisar Factory Blast: The police and the fire service officials have reached the spot.

At least five people were killed and seven injured in a huge explosion at a chemical factory at Boisar in Maharashtra's Palghar district, over 100 km away from Mumbai, a police official said on Saturday.

The under-construction plant of Ank Pharma, where the explosion took place, is located in a Maharashtra Industrial Development Corporation (MIDC) area at Kolwade village, the official said.

The blast, which took place during the testing of some chemicals around 7:20 pm, was so huge that it was heard 15 km away, and shattered windows of some houses in the area, news agency PTI reported.

The under-construction plant building collapsed after the explosion.

At least seven injured people were rescued from debris, the police said.

A fire started after the blast but it was put out, he added.

Chief Minister Uddhav Thackeray announced assistance of Rs 5 lakh each for the relatives of those killed, a statement from his office said.

The chief minister was monitoring the relief and rescue operation himself, it added.

A National Disaster Response Force (NDRF) team had been called for rescue operations, officials said.

(With inputs from PTI)