Investigators are working hard to locate the eight kilogrammes (17.6 pounds) of uranium, warning that it poses a health risk to people who may come in contact with it, the China Daily said.

From April 2005 until January this year, the four -- including a uranium mine owner surnamed Zhou -- tried to find buyers for the uranium, described as the two common isotopes U-235 and U-238, according to the paper.

Those types can be used to produce nuclear weapons.

The four eventually met a businessman, surnamed Peng, who promised to introduce them to a Hong Kong buyer willing to pay 1.6 million yuan (210,000 dollars) per kilogramme, it said.

However, Peng turned the four into the police, and they were caught in January this year carrying a sample, according to the report.

In China, illegally trading in uranium can be punished by death, the paper said.

The four told investigators they were unable to say where the uranium was, claiming it had been lost while circulating among a large number of potential buyers.

However the Tianhe District Court in Henan province, where the men are on trial, said the case will remain open and that a verdict would not be delivered until the uranium was found.

Exposure to uranium for a lengthy period of time can lead to leukaemia and other cancers.