The workers have real grievances, and they seem to be committed to continuing the protests

Han Dongfang, Chinese labour activist

Han Dongfang, a Chinese labour activist based in Hong Kong, said that the authorities had readied paramilitary police and a military tank unit, but that there had been no confrontations.

The BBC Beijing correspondent says this is one of the biggest labour protests in China in recent years.

An oil company official said the protests were the result of a misunderstanding and "should be resolved soon".

A local official confirmed that the demonstrations had been going on, but said the police were not interfering.

Redundancies

Reports said the workers were protesting against cuts in severance pay and heating subsidies promised them when they were sacked three years ago, and an increase in unemployment insurance premiums.

"The workers have real grievances, and they seem to be committed to continuing the protests until those grievances are addressed," said Mr Han.

Dongfang said the army had been readied

Mr Han's organisation, the Chinese Labor Bulletin, says the workers have set up their own independent union.

This is illegal in China, where workers can only seek redress through official unions controlled by the Communist Party.

Daqing oil field is China's biggest, and opened in the 1950s.

It was long-promoted as a symbol of China's revolutionary industrialisation, employing some 300,000 workers at its height.

But the Daqing fields are now well past their peak, revenues are falling and thousands of workers have been sacked in recent years.

Our correspondent says labour unrest is growing across China as economic reforms force decrepit state run industries to lay off millions of workers.