China, North Korea's main ally, has said it firmly opposes Pyong- yang's nuclear test and strongly urges the reclusive state to cease any action that will heighten tensions in the region.

The Foreign Ministry said Beijing will also lodge a protest with the North Korean embassy over the test, which shook parts of China's north-eastern provinces.

China's strong stance was widely reported by the state media, and the Xinhua news agency said the North's act has "introduced new uncertainties to the already delicate and complicated geopolitical security situation".

Beijing often opposed imposing sanctions on Pyongyang at the United Nations Security Council. But in April, it agreed to a ban on imports of coal, iron ore and other commodities from the North, which had conducted a nuclear test in January. According to Chinese government data, the ban accounts for more than 40 per cent of North Korea's total exports to China in US dollar terms.

Foreign Ministry spokesman Hua Chunying yesterday reiterated that China is committed to a nuclear-free Korean peninsula and will prevent the spread of nuclear weapons and safeguard peace and stability in North-east Asia.

At the same time, China "strongly urges all parties to focus on the big picture" to prevent further provocations, Ms Hua added.

"China will continue to conduct talks and dialogue under the framework of the six-party talks process to resolve issues on the Korean peninsula," she said.

Started in 2003, the now-suspended six-party talks bring together North and South Korea, Japan, China, the United States and Russia with the aim of denuclearising North Korea through negotiations. Hosted by China, the talks have made little progress as the North continued to conduct nuclear tests.