A major fire broke out at the Haldia Petrochemicals Ltd’s (HPL) plant here on Friday, leaving 13 staffers injured in one of the worst accidents in the firm’s 19-year history.

The 13 injured persons, three of whom are said to be in critical condition, have been brought to Calcutta. Some of those injured are managerial-rank employees.

A gas leak at the plant’s naphtha unit is suspected to have sparked the blaze. The management held an emergency meeting and sources said the plant might have to be shut unless the source of the gas leak was detected quickly and contained.

Fourteen fire engines were rushed to the plant amid conflicting reports whether the blaze had been fully contained. The board of HPL held an emergency meeting on Friday afternoon to take stock of the situation.

The fire broke outside in the naphtha cracker unit during a round of repairs. HPL manufactures polymers used in plastic material and certain chemicals.

“It appears there was a gas leak. Sparks from ongoing welding work caused the gas to catch fire. There were supervisors to oversee the work,” a source said, adding the incident seemed to have been caused by a human, rather than mechanical, error. It was not clear till Friday night how the leak occurred.

HPL is one of the largest manufacturers of polymers in India and the biggest in the east. It is owned mostly by The Chatterjee Group, while the Bengal government has a significant minority stake.

HPL’s general manager (human resources) Debasish Sen declined comment on the cause of the fire, saying he was busy supervising treatment of the injured in hospitals.

“We will begin an investigation soon to find out the cause of the accident,” another HPL official said.

Haldia sub-divisional police officer Tanmay Mukherjee said the injured were rushed to Calcutta with “green corridor escort”, during which roads are sanitised and cleared to allow unimpeded movement of emergency services.

Soumen Naik, a casual worker who was not on duty on Friday but was in the vicinity of the plant when the blaze started, said: “I heard a loud bang around 11am, followed by a tower of flame. I heard later that my colleagues had to be rushed to Calcutta, around 120km away, because there is no burn unit in Haldia (hospitals) despite the presence of so many industrial units. They lost valuable time.”

Later on Friday evening, HPL issued a statement.

“The HPL board, at its meeting held this evening, has been apprised of the current situation. While expressing their regret over the incident, they have authorised the management to take all appropriate action for the welfare of the injured and provide support to their families. The board also recorded its sincere appreciation of the state government’s prompt assistance and facilitation that has helped the management to reach the injured in a relatively quick time frame to Calcutta,” the statement noted.

HPL has faced mishaps earlier, causing loss of life, including one last year.