This handout photograph taken and released by the Russian Emergency Situations Ministry on October 22, 2021, shows firefighters working to put out a fire at a gunpowder and chemicals plant in Ryazan Region. AFP
The government of the Ryazan region, where the factory is based, said they had died in the factory blaze in the village of Lesnoye, 300 kilometres (180 miles) from the capital.
"The fate of one person remains unknown," it said in a statement.
One more person was hospitalised with "major burns" and is in a "serious condition", it added.
The emergencies ministry published images showing smoke and debris at the severely damaged factory building.
Earlier it said the fire could have broken out as a result of "violations of technological processes and safety measures" at the local PGUP Elastic factory
The plant is considered a "strategic company" by the Russian government.
According to its website, it belongs to state conglomerate Rostec which brings together a range of companies supplying industrial or high-tech products to civilian and military sectors.
But local media said it went bankrupt in 2015 and that its workshops were used by other companies of the explosives sector.
Firefighters first received a report that a fire had broken out at the plant at 08:22 local time, the emergencies ministry said.
It dispatched its acting head Alexander Chupriyan to the site. He is in charge of the ministry after its chief Yevgeny Zinichev died falling off a cliff during Arctic exercises last month.
Russia's Investigative Committee, which probes serious crimes, said it had sent detectives to probe if the factory had complied with "industrial safety levels".
More than 170 rescuers were working in the area, it added.
The head of the local administration earlier told the TASS news agency that 17 people were inside the plant's workshop at the time of the fire.
Concerns Over Safety Standards
Authorities said the blaze -- which covered an area of 160 square meters -- had been put out and did not pose a danger to locals.
Amateur video footage on Russian social media showed rows of fire trucks at the scene with burning debris in a wooded area by the factory.
Accidental fires are common in Russia, where hundreds of blazes are recorded each year due to ageing and dilapidated infrastructure and non-compliance with safety standards that are often lax.
In Russia's worst fire disaster in recent memory, an inferno at a shopping centre in the Siberian city of Kemerovo in 2018 left 64 people dead, including 41 children.
Investigators said that blaze resulted from "flagrant violations" of safety norms including emergency exits locked and non-functioning alarm systems, prompting President Vladimir Putin to demand answers.
Authorities in the aftermath found that hundreds of commercial and cultural sites across the country fall below fire safety standards.
Government critics say graft is at the heart of safety rules being violated more broadly as building permits are given by officials in exchange for bribes.
More recently, 11 people were killed in December 2020 at a retirement home in the Urals region of Bashkortostan that officials said was operating over capacity limits.
After a huge blaze at a historic factory in Saint Petersburg in April 2021, investigators said the site had a number of violations for fire safety and that management had continued operating despite being aware of them.