Four people choked to death after they inhaled a toxic gas in a pharmaceutical plant in this Maharashtra district Tuesday, police said.

At least five people were injured.

The accident happened in Sequent Scientific Ltd in Boisar town around 7.30 p.m. when there were 17 people working in the plant.

"According to preliminary investigations, a pipe burst caused leakage of hydrogen sulphide gas in the plant premises," Boisar Police Station in charge U.D. Sonawane told IANS.

While four who inhaled the gas died shortly thereafter, at least five others were rushed to the local civil hospital, he said.

While two continue to remain critical, the other three are out of danger, according to Sonawane.

The victims have been identified as Shivkant Tiwari, Binoo Sinh, Naresh Yadav and Sarvesh Kumar.

The plant is located in the Maharashtra Industrial Development Corporation's industrial area of Boisar and further investigations are on to find out the cause of the gas leak.

Boisar is around 100 km north of Mumbai in the industrial belt of Thane district.