As China and Russia work together to build a cross-border natural reserve for Siberian tigers, Hunchun in Jilin province has become a migration hotspot for Siberian tigers, the World Conservation Society said on Tuesday.

Liu Peiqi, director of the WSC China program, said the population of Siberian tigers in Hunchun, which borders Russia and Democratic People's Republic of Korea, has doubled from three in 1998 to six or seven in 2012.

"The frequent traces left by adult females and small cubs are especially encouraging," Liu said.

The Siberian tiger is the biggest existing feline. Dubbed the "king of the forest", it has a strong and agile body, and is also the most colorful of all existing tiger species.

The global wild population of Siberian tigers is estimated at less than 500, with more than 90 percent living in Russia. China is home to around 20 in Heilongjiang and Jilin provinces.