An explosion at a Russian factory in the Urals has left at least 10 people dead, the region’s governor has said.

Alexei Teksler said at least 19 people had also been injured in the blast, which took place in the Kopeisk district of the Chelyabinsk region, which borders Kazakhstan.

The governor did not say which factory had been hit, but verified video shows a fireball filmed from the road beside the Plastmass plant in the area. Local media reports that the factory produces ammunition and weapons for the Russian military.

Authorities have not said what caused the blast, but Teksler stressed that the incident “was not a drone attack”.

The fire – which was first reported late on Wednesday – has since been extinguished, and a search and rescue operation at the plant was ongoing on Thursday morning, Teksler said.

The whereabouts of 12 members of staff was still unknown, he added.

Friday has been declared a day of mourning in the region and investigators have opened a criminal inquiry into the blast.

BBC Verify has located two videos of the explosion. One is CCTV showing the moment of the blast, captured around 3km (1.9 miles) from the site. The other shows the fireball filmed from a car driving down an adjacent road.