Indian authorities on Thursday ordered an inquiry to determine within seven days the cause of a blast at a coal-fired power plant that killed 26 people and injured more than 100 — one of the country’s worst industrial accidents in years.

More than 20 survivors were battling for life with severe burn injuries following Wednesday’s blast at the 1,550-megawatt plant operated by state-owned NTPC in northern Uttar Pradesh state, state officials said.

Arvind Kumar, a principal secretary, said some of the severely injured had been taken to a hospital in the state capital Lucknow.

“Blockages in the flue gas pipe in a unit led to the blast. Hot flue gases and steam let out by the blast severely injured several workers,” Sanjay Kumar Khatri, the top government official of Rae Bareli district where the plant is located, told Reuters on Thursday.

“A magisterial inquiry has been initiated. This two-member technical team will submit findings within seven days,” Khatri said.

NTPC is the country’s top power producer and accidents have been rare at its facilities.

Senior state police official Anand Kumar said in a statement posted online on Wednesday that ash had piled up in the furnace beneath the boiler, which led to building up of pressure resulting in the explosion.

The state government has offered cash compensation of 200,000 rupees ($3,097) to the families of the deceased, 50,000 rupees for the severely injured and half of that to those who sustained minor injuries, Khatri said.

The plant in the town of Unchahar supplies electricity to nine states, NTPC’s website showed. But the company said other facilities would make up for the shortfall and outages were unlikely.

The 500 MW unit, where the mishap occurred, had been operating since April and is under shut down after the accident. The other five units of the station are operating normally, NTPC said in a statement.

“This is most unfortunate. NTPC has initiated an inquiry into the incident. We are not a company that will take any risk. We have so many units that if power cannot be supplied by one, it can be given by the other. It was a sudden accident,” an NTPC official, who did not wish to be quoted, said.