BEIJING, Oct 28, 2008 (AFP) - A UN agency called Tuesday for China to immediately disclose if an industrial chemical found in dairy products had been used in livestock feed and contaminated the wider food chain.

The recent discovery of melamine in mainland chicken eggs sold in Hong Kong has triggered worries that the chemical was present in a wide range of foods such as farm-raised meats and fish, a UN official said.

Zhang Zhongjun, programme officer with the UN Food and Agricultural Organisation, told AFP that China's agriculture ministry was investigating the possibility that melamine had been mixed into farming feed.

"But we do not know the details of the investigation... we want them to immediately report to us the results of their findings," Zhang said.

"If the feed is found to be contaminated, then there is the possibility (that pork, chicken, fish and beef could also be contaminated)."

Zhang said that feed producers could have laced their products with melamine to falsely boost protein content, similar to the methods of milk producers in a scandal that has left China's dairy industry in shambles.

Four children have died of kidney failure and 53,000 fallen ill in China this year after drinking milk or consuming dairy products laced with melamine, which is usually used in making plastics and fertilisers.

The dairy scandal has expanded worldwide with governments around the world recalling or banning Chinese products with milk content.

Hong Kong's Centre for Food Safety announced over the weekend that eggs produced in northeast China were found to be tainted with melamine.

The findings led Hong Kong to expand its testing of food imported from China to pork, farmed fish and offal products.

A food safety official in Dalian city near where the tainted Hong Kong eggs were produced said Monday melamine had been detected in eggs last month.

The tainted eggs were then destroyed, he said, without disclosing the quantity.

"We checked eggs in September and when we checked again in October, no melamine was found in eggs," the official told AFP on condition of anonymity.