Floodwaters on the Nen river in northeast China have burst a dike, threatening the nearby Daqing oilfield - the country's largest, a local official and Xinhua news agency said Friday.

Workers at the million-barrels-per-day Daqing oilfield were working round the clock to build new flood defenses after the raging Nen ripped a 1,640-foot hole in a dike on Friday morning, the official said by telephone."The breach is too big so it can't be blocked," the official said. He declined to provide further details.

The official Xinhua news agency said most of Daqing's nearly 20,000 wells were still operating normally.

Daqing said on Thursday it closed more than 1,000 oil wells because of waterlogging after recent floods, but an official declined to say what impact the closures would have on output.

More than 20,000 people were evacuated from the area before the dike burst and some 200,000 people were working on Daqing city's flood defenses, Xinhua said.

Dikes near Daqing have been reinforced with 11.38 million sandbags and 175.4 miles of secondary dikes have also been reinforced, Xinhua said.

Daqing oilfield produces more than 50 million tons of crude oil annually, accounting for more than one-third of the nation's total petroleum output.

In 1969, a flood hit the oilfield causing a number of deaths, but oil production did not stop, Xinhua said.

State media on Friday kept up an appearance of high morale among flood workers and lavished coverage on a visit by Chinese President Jiang Zemin to key Yangtze dykes in Hubei province.

"Decisively engage to the end - persist, persist and persist again - and we will definitely achieve the final victory in our emergency struggle against the floods," the People's Daily quoted Jiang as saying.