NEW DELHI (Reuters) - An explosion at an Indian power plant killed 20 people and injured up to 100 in the northern state of Uttar Pradesh on Wednesday, authorities said, in one of the country’s deadliest industrial accidents in years.

More than 20 survivors suffered severe burns in the blast in the coal-fired plant operated by state-run NTPC, and casualty numbers would probably rise, state police said.

The 1,550-megawatt (MW) plant in the town of Unchahar supplies electricity to nine states, according to NTCP’s website. But the company said other facilities would make up the shortfall and outages were unlikely.

“Ash had piled up in the furnace beneath the boiler, which then led to building up of pressure resulting in the explosion,” senior state police official Anand Kumar said in a statement posted online.

India’s largest power producer said there was a “sudden abnormal sound” at a unit around 3:30 p.m., and flue gases and steam escaped.

The company said the blast hit a 500-MW unit that had been operating since April. Three other units with a combined capacity of 630 MW were continuing to operate, it added.

Around 90-100 people were injured, Uttar Pradesh’s top bureaucrat handling law and order, Arvind Kumar, told Reuters.

Police said 20 people have been confirmed dead by the district administration.