A highly radioactive lead ball has gone missing in China, prompting authorities to launch an urgent search.

The dangerous radioactive lead ball, containing Caesium-137, is a major component of a nuclear scale.

The scale, used to make precision measurements, was found to be missing on Monday after workers began dismantling a cement factory where it was used in Tongchuan city in northwest Shaanxi province.

An official report does not say how much Caesium-137 is missing but warns that only a tiny amount can damage the human nervous system and lead to death.

The material could also explode if it comes in contact with water.

The provincial environmental protection agency and police have issued urgent orders to find the radioactive material, which may have been buried in up to 5,000 tonnes of scrap waste or melted down.

In a later report, state news agency Xinhua said environmental officials had found Caesium-137 radioactivity at a steel refinery in Shaanxi's Fuping county, but it is not yet known whether the incidents are linked.

The steel refinery had bought 265 tonnes of scrap metal from the dismantled cement factory and had already melted it down.

Police and environmental officials have spread out to all scrap metal yards and several steel refineries in the area and are testing for radioactivity.