China has bought the rights to use a North Korean port, state media reported Tuesday, giving Chinese exporters access to the Sea of Japan and bringing much needed income to Pyongyang.

The state-owned Yanbian Haihua Group bought the rights to use two wharves at Chongjin port, on North Korea's east coast, for 30 years after setting up a joint venture company worth $7.83 million, the Global Times daily reported.

The port, on the Sea of Japan, which is known to Koreans as the East Sea, is close to the Rason economic zone, near North Korea's borders with Russia and China.

Impoverished North Korea is striving to revitalise its economy through foreign investment in its economic zones, while China, its sole major ally, has repeatedly urged the country's leaders to open up to the world.

The two countries agreed to push forward the development of special North Korean economic zones near the Chinese border when new leader Kim Jong-Un's uncle Jang Song-Thaek visited Beijing last month to beef up economic ties.

Jang -- the husband of late leader Kim Jong-Il's sister Kim Kyong-Hui -- is seen as a key figure in the North's power elite who supports the young and inexperienced Jong-Un, believed to be in his late 20s.

South Korean news agency Yonhap said in February that China would invest about $3 billion (2.4 billion euros) in developing a free trade zone around the northeast port of Rason bordering China and Russia.

North Korea and China are jointly also developing the Hwanggumphyong and Wihwado zone on two islands in the estuary of the Yalu river that marks their border. Ground was broken in December.