Pavel Malkov, governor of the Ryazan region that lies just southeast of Moscow, said last Friday that the incident had been triggered by a fire breaking out inside a workshop at the factory.

But it was unclear from Russian media reports what caused the fire or what the factory was producing. Official Russian sources gave no details beyond efforts to find and treat the injured.

Some media reported that it was a explosives plant but Reuters was unable to immediately verify that information.

“As of Aug 18, 20 people died as a result of the emergency incident,” the local emergency service headquarters said in a post on Telegram.

“There are 134 injured, of whom 31 patients are in hospitals in Ryazan and Moscow, while 103 patients are undergoing outpatient treatment.”

Video footage released by the emergencies ministry showed parts of the plant completely destroyed, with rescuers working through giant piles of rubble with sniffer dogs.

In another video, psychologists were shown working with local residents to provide counselling.