A fire at a petrochemical plant in eastern India injured at least 20 people, five of them critically, police said.

The blaze broke out Tuesday in a naphtha pipeline at a facility operated by Haldia Petrochemicals and quickly spread to nearby homes in West Bengal’s Purba Medinipur district, about 130 kilometers (80 miles) southwest of the state capital, Kolkata.

Firefighters used 12 fire engines to bring the blaze under control, while the injured were rescued and taken to nearby hospitals, police said. The injured included plant workers and at least two security guards.

Video from the scene showed firefighters dousing the blaze with water as thick black smoke rose from the burning pipeline.

Naphtha is a highly flammable petroleum product used in the production of fuels and other chemicals.

The cause of the fire was not immediately known.

Haldia Petrochemicals said in a statement it was investigating the incident.