DANDONG, China, Oct 18 (Reuters) Chinese customs agents checked papers and trucks on the border with North Korea today, but there was no sign of increased scrutiny despite UN sanctions over the North's reported nuclear test.

China joined in the UN Security Council's 15-0 approval of a US-drafted package of financial and weapons sanctions against North Korea, its old Communist ally and trading partner.

But Beijing made clear it would not conduct searches of cargo going to and from North Korea for material that could be used to produce weapons of mass destruction.

President Hu Jintao has been quoted as saying the sanctions should be implemented in such a way that they don't escalate the situation into something uncontrollable.

Beijing has long feared action against its neighbour that could push the poor and highly militarised state into collapse, potentially sending a wave of refugees across the border.

In the northeastern city of Dandong, cargo trucks rumbled across the Friendship Bridge that spans the Yalu River between the two countries and there appeared to be no slowdown in trade.

Officials checked drivers' papers and opened the backs of trucks to look inside. But none was seen unloading or thoroughly inspecting cargo, and most trucks were through the checkpoint in no more than a minute or two.

Traders in the border city, where most signs are in Chinese and Korean, spoke of some tightening of controls, but many also said little had changed since North Korea defied international warnings and conducted a nuclear test last week.

One woman said her company's regular shipments of cabbages, carrots and turnips to North Korea were continuing without problems, but that a shipment of extract oil sent last week had not gone through.

''You need to have a certain permit -- then you can sell that kind of thing,'' said the woman, who did not want to be named.

An official from the local trade bureau had come by to inform her company that any energy products for export required the permits, the woman said, indicating that China was now enforcing the long-standing regulation.

''Trade through the bigger companies is still going on, but its harder for the small businesses now,'' said another trader.

Some branches of Bank of China have halted remittances to North Korea, Japanese media has reported, and some Chinese businessmen spoke of difficulties with fund transfers.

But many in Dandong said the days since the nuclear test had brought a lot of chatter, but little discernible change.

''There are lot of rumours about customs inspections and boat inspections, but we haven't seen any difference,'' said a woman surnamed Xu, whose company imports paper products from North Korea.

Outside of the city, in places where the river narrows and the distance between the two countries, whose relationship was once described as close as lips and teeth, is literally a stone's throw, a fence is being erected.

Locals say the fence -- cement pillars about two metres high strung together with barbed wire -- has only been recently built.

But there was no visible security presence along the fence and little signs of tension, only muddy fields and rows of corn drying as the winter frosts set in.

''Who knows,'' exclaimed Xiao Wang, out for a pleasure cruise on the river between the two countries, when asked if anything had changed between China and North Korea.

''Maybe there have been some changes in relations, but they'd all be military secrets,'' he said. ''We wouldn't know.'' REUTERS AB HS1629