Some tension, but trade uninterrupted at China-N Korea border

A day after North Korea said it exploded a nuclear device at a site near the Chinese border, security was tighter but there was no obvious sign Beijing's anger at the test had translated into any action to stem trade with its isolated neighbour.

China is North Korea's main economic and diplomatic backer, and expressed anger with Pyongyang for the test. Beijing said it had not received any prior warning.

Security was tighter than usual and officials were skittish on Thursday at Tumen, a border crossing on the remote northeastern end of the frontier, but trucks were regularly crossing the bridge across the frozen Tumen River that divides the two countries.

Uniformed military personnel, as well as plainclothes police, dotted the boundary and prohibited tourists and locals from taking photos of North Korea.

Chinese children ice skated at a pond overlooking the border, but very few North Koreans could be seen in the village on the other side.

Security officials briefly detained two Reuters reporters near the border and ordered them to leave by train.

China has signed up for tough United Nations sanctions on North Korea and insists it follows them, including carrying out border inspections, but China also provides large amounts of aid off the books to Pyongyang, experts and diplomats say.

Still, a nuclear-armed North Korea is not something Beijing wishes to see.

The official China Daily newspaper said in an editorial there would be "no tolerance and compromise" from Beijing when it came to North Korea's pursuit of a nuclear arsenal. "By refusing to engage in any meaningful talks for years, and by playing the nuclear card time and again, the DPRK (North Korea) is only alienating itself further from the international community," the paper said.

China fears North Korea's nuclear programme destabilises its neighbourhood and gives the United States a pretext to send weapons and forces to the region.

But many Chinese experts fear that if China pulled back support for its neighbour, it could destabilise the country and send a flood of refugees into China.

Xie Tao, a North Korea expert at Beijing Foreign Studies University, said if China dramatically changes courses with North Korea it would raise questions about historical mistakes made by the Chinese Communist Party.

"We fought a war," he said, referring to the 1950-53 Korean War in which China sided with North Korea. "Half a million Chinese people died, and now you say sorry, we made a terrible mistake. If you made that terrible mistake, are there any other terrible mistakes that you made since 1949?"

At the border, however, the concern was more about the environment. "I'm worried about the health impacts. The test was so close to us, and a nuclear bomb is a dangerous thing," said a man surnamed Liu outside a train station in Tumen, just about 200 km (120 miles) from North Korea's nuclear test site.

"Right now I feel a little afraid," said Piao Yanjin, 23, an ethnic Korean student at Yanbian University in Yanji, a nearby town. "If they're going to carry out even larger-scale nuclear weapons tests, this will definitely harm our lives. We should definitely think of more ways (to prevent it)," Piao said.