BEIJING -- North Korea's latest act of provocation could push China to toughen its already unusually hard stance towards its communist ally which could even face sanctions from its patron, say observers.
They believe Beijing is already shifting its policy as it sees a belligerent Pyongyang as a liability to its superpower aspirations.
Also, there are fears that a nuclearised North could give the United States more reasons to deepen its presence in Asia, which could be used to curb China's rise.
"China is likely to react harshly towards North Korea," said Singapore-based analyst Li Mingjiang.
"In addition to working with the international community to censure and punish North Korea, China will very likely impose its own sanctions on Pyongyang, for instance, by significantly reducing food and energy assistance."
Signs of a harsh response were seen yesterday, with Chinese Foreign Minister Yang Jiechi summoning the North Korean envoy to register a stern protest over Pyongyang's nuclear test, in a meeting described as "unprecedented" by Xinhua news agency.
This follows recent tough talk and actions by Beijing against Pyongyang for its rocket launch last December.
State media had been running editorials threatening a "heavy price" and a cut in Chinese aid if Pyongyang conducted its third nuclear test since 2006 and 2009.
China's Foreign Ministry last month castigated the North for spending funds on its rocket and nuclear programmes instead of on the economy. Beijing has also backed tougher United Nations sanctions against the North.
Another reason for Beijing's harder stance is its need to show who is boss to the only country it has inked a security treaty with -- in 1961 -- which compels them to provide military aid if either side comes under attack.
While many believe the nuclear test was timed to mark the anniversary of the February 16 birthday of late North Korean leader Kim Jong Il, some believe holding it on the third day of the Chinese New Year celebrated across China also carries a specific message for Beijing.
Said Professor Li: "The message to Beijing is this: No matter what, Pyongyang would not allow its relations with Beijing to determine its policy on the missile and nuclear programmes."
He said the North knows from past experience that Beijing is unlikely to abandon Pyongyang, out of fears that a regime collapse could lead to an influx of refugees on China's north-eastern borders.
East China Normal University foreign policy expert Yang Cheng also believes the latest development could see China make further tweaks to its North Korea policy because a nuclearised Pyongyang "is not a good thing" for Beijing.
This is because the nuclear test will raise tensions in a region already roiled by territorial disputes between China and Japan, and Japan with South Korea, he added.
Also, Japan and South Korea could attempt to counter the North's threat, by seeking nuclear weapons themselves -- an extreme scenario that China wants to prevent, said Professor Yang.
But not all believe China will change its North Korea policy.
Said US-based analyst Bruce Klingner of The Heritage Foundation: "We hope China will move towards allowing meaningful sanctions, but we've heard these kind of messages before."
He said extensive sanctions are needed against the North and also second-level violators such as banks and businesses to signal to China that condoning Pyong-yang's actions would create the crisis Beijing wants to avoid.
But it is not all up to China as North Korea is not its puppet, said Peking University analyst Wang Dong. He said: "While China might have some leverage over the North in trade and aid, China's options are limited as well. I believe a multilateral approach is necessary for addressing the North Korea challenge. No one can deal with that by itself."