Five people were killed and seven were injured in a blast at Cochin Shipyard in Kerala on Tuesday afternoon.

The blast took place on board the Oil and Natural Gas Corporation’s drill ship Sagar Bhushan around 9.15 am when it was brought to the dry dock for repairs, Cochin Shipyard Limited said.

At the time of the blast, workers were engaged in welding around the potable water tank of the ship, The Indian Express reported. The shipyard’s Chairperson and Managing Director Madhu S Nair said the explosion could have occurred due to “gas consolidation [inside the tank]”. The exact reason would, however, be known after a detailed investigation, he added.

Kochi City Commissioner of Police MP Dinesh confirmed the toll. The deceased were identified as senior fireman Unnikrishnan CS, fire watchman Jayan KB, safety assistant Gibin, and contract workers Ramsheed and Kannan MV.

The injured have been shifted to a hospital, and one of them, Sreerop, has suffered 45% burns and is in a critical condition. The others are out of danger, Nair said.

The company said that it would pay the relatives of those who died in the blast Rs 10 lakh. “All treatment expenses of the injured will be met by the company as per the existing policies,” it added.

Union Shipping and Transport Minister Nitin Gadkari has ordered an inquiry into the blast. In a tweet, Gadkari said he has asked the Cochin Shipyard to “provide all necessary medical support to victims” and begin an inquiry immediately.