Chinese social media users berated authorities Wednesday for their relatively mild response to North Korea's nuclear test, with one likening Pyongyang to a "crazy dog" that had humiliated Beijing.

The hostility towards China's defiant neighbour contrasted with the official response from Beijing -- expressing "firm opposition" but reiterating calls for calm and restraint and not mentioning any reprisals or sanctions.

Pyongyang conducted the test on Tuesday, two days after Lunar New Year, which is China's biggest annual festival, and as the public holiday continued.

"If you pursue an unjust long-term diplomatic policy, then people will dare to explode a stinkbomb at your door while you are on holiday," said Yu Jianrong, a director at the Chinese Academy of Social Sciences.

"You are inviting your own humiliation," he added on Sina Weibo, China's popular Twitter-like service, where he has 1.5 million followers.

Beijing is Pyongyang's most important backer, providing it with trade and aid that have enabled the state to survive since the end of the 1950-53 Korean War.

China fears instability would bring refugees flooding across the border, or even ultimately a unified Korea with a US military presence on its doorstep.

But an online commentator using the nickname Wuyuesanren slammed some suggestions that North Korea's nuclear programme strengthened China's security, likening Beijing's policy to "keeping a crazy dog to guard the house".

Xie Wen, a former manager at Yahoo China, urged Beijing on his Weibo account at least to abandon a 1961 treaty of mutual assistance, cancel all aid and military or security cooperation and recall China's ambassador.

North Korea "simply doesn't trust China and is not willing to be inhibited by China", wrote Weibo user Zhuanshengben. "For China alone to emphasise China and North Korea's so-called friendship, this is the ultimate stupidity."

One user called Long Can supported the use of military force against North Korea, saying that "if America mobilises troops against North Korea, I will give its government my entire year's salary".

Meanwhile on Twitter -- which is blocked in China -- one of the country's most prominent dissidents, Hu Jia, called China and North Korea "the most despicable big rogue and ruthless little rogue".

He posted a recording of a phone call he said he made to the North Korean embassy in Beijing, in which he told them: "I just want to say, I am Chinese citizen Hu Jia, and I want to express my opposition to your carrying out a nuclear test."

"What?" came the response from the embassy. "Are you out of your mind?"