The Siberian tiger has been increasing its range from the China-Russia border area, moving deeper into northeast China, the World Wildlife Fund (WWF) said Thursday.

The expansion comes as China does more to protect natural forests and rehabilitate tiger habitat, according to Chang Youde, a senior manager with the WWF China big cat program.

"Living space for the big cats is saturated in Russia where around 540 now live," said Chang on Thursday at a conference on tiger conservation.

Long-term monitoring has shown tigers moving from Hunchun nature reserve on the Russian border to Wangqing and Huangnihe nature reserves in Jilin Province, some distance from the frontier. Six have been spotted in Huangnihe in recent years and three are known to be resident there, according to Li Cheng, head of the reserve.

Jilin forestry department has set up about 1,000 remote infrared cameras to monitor Siberian tiger and Amur leopard since 2006. Best estimates are that there are 27 tigers and 42 leopards in Jilin. Jilin banned commercial logging in key state forests last year.

A 10-year government plan on tiger protection and leopards in Jilin is under consideration, with more protection zones set to be established to complement the current six. Around 8,000 square kilometers of suitable habitat could accommodate more than 30 Siberian tigers and over 50 Amur leopards.

People living in designated reserves will be relocated, with substantial curbs on grazing and logging, according to the provincial government. Strong measures will be taken against poachers.

Rohit Singh, chairman of the Rangers Federation of Asia, said he was amazed by what China has done to protect tiger habitat and the subsequent rise in numbers.

Siberian tigers, listed as endangered by the International Union for the Conservation of Nature, live in east Russia, northeast China and northern parts of the Korean Peninsula.