The Russian national flag flies at half-mast on top of the State Hermitage museum in central St Petersburg on Tuesday to mourn the victims of Monday's blast in the city's metro. Photo: AFP

A French doctor has bequeathed $3,639 to cats living in the basement of the Hermitage museum, a world-renowned gallery in Russia's Saint Petersburg.

The money was left by French doctor Christophe Batard, who died at the age of 51. "Our French friend has done a remarkable thing... and it is such a beautiful gesture," Hermitage's director said. 

He proposed the amount left to the cats be put towards improving the basement where they live.

The history of the Hermitage cats dates back to the 18th century when the museum, then called the Winter Palace, was an imperial residence in Russia's former capital. 

Now the Hermitage is home to nearly 70 cats that officially hunt for rodents beneath Russia's largest museum.