Floods raged in northeastern China on Saturday, while swollen rivers crushed levees and threatened a major industrial city with its worst disaster in almost 50 years.

Heavy rains in Heilongjiang Province, which borders Russia, were expected to bring the worst floods since 1949 to the provincial capital of Harbin, the state-run Xinhua News Agency reported. A flood crest expected Friday could exceed danger levels by 7 feet, Xinhua said.No casualties were reported from the collapse of a second dike near Daqing, a city of 2.3 million and China's largest oil field. The breach forced the evacuation of about 3,850 people, Xinhua said.

President Jiang Zemin urged the nation to rally together in the fight against summer floods that have affected one-fifth of the Chinese population, killing more than 2,000 people and leaving millions homeless.

Flooding began along the lower reaches of the Yellow River, which runs across north-central China. The Yellow River has been the source of particularly disastrous floods over the centuries.

Jiang, who traveled earlier this week to flooded areas along the Yangtze River farther to the south, warned that after more than six weeks of flooding, the disaster was reaching a "crucial stage."

Millions of people have been stranded on sweltering dikes along the raging Yangtze River with minimal shelter, clean water or food. Jiang urged relief workers to ensure social order and guard against the spread of diseases, Xinhua said.

The State Council, China's Cabinet, issued an urgent order Saturday warning that more had to be done to prevent disease.

"Historical experience tells us that major disasters often lead to epidemics," said the order carried by Xinhua.

Government officials insist that apart from a few outbreaks of infectious diseases, no epidemics have occurred in flooded areas.

Thousands of medical teams are handing out food, water purification tablets and medical supplies.

But shortages of funds are delaying relief efforts, the Red Cross said.

Meanwhile, state radio reported that Li Peng, chairman of the National People's Congress and former premier, had traveled to Heilongjiang Province to observe the flood fight along the Nen and Songhua rivers.

At Daqing, which produced about half of China's oil last year, 355 of the oil field's 20,000 wells were waterlogged due to flooding, Xinhua reported. Soldiers and residents had abandoned efforts to repair dikes that burst Friday and Saturday, and were concentrating on shoring up other levees protecting the oil field.