A gas explosion has caused a fire at the State Research Centre of Virology and Biotechnology near the Russian city of Novosibirsk.
The facility, known as Vector, houses dangerous viruses ranging from smallpox to Ebola, Russian authorities have said.
The blast took place on the fifth-floor during repairs being made to a sanitary inspection room, Vector revealed on Monday. The site was developed during the 1970s to create biological weapons during the Soviet era, as well as means of protection against them. It is now one of Russia's main disease research centres.
Russian authorities have said that the room were the gas explosion occurred was not holding any hazardous substances and no structural damage was caused.
One worker at Vector has been hospitalised after suffered three-degree burns from the blast. The fire covered 30 square metres and has since been extinguished.
The smallpox virus survives in two places on Earth, at Vector and at another high-security laboratory at the US Center for Disease Control in Atlanta.
In 2004, a researcher died at the laboratory facility after accidentally pricking herself with a needle that carried the Ebola virus.