​A explosion caused a fire at a Russian research lab that is one of two facilities in the world to keep samples of the deadly smallpox virus.

The blast happened Monday during repairs at the Russian State Center for Research on Virology and Biotechnology — known as Vector — near the Siberian city of Novosibirsk, the Russian news agency Tass reported.

A construction worker was injured and hospitalized in intensive care for burns.

The report, citing a statement from Vector, said no biohazards were being stored in the room and there is no threat to the surrounding population.

The building did not suffer any structural damage.

The lab, founded in 1974, works to develop vaccines against swine flu, HIV and Ebola.

Other than Vector, the only location where smallpox samples are stored is the Centers for Disease Control and Prevention in Atlanta, Ga.