Seventy houses in a village in Antu were destroyed, while 570 families in a mountain valley had to leave their homes after the area was submerged beneath 20 metres of water.
Flooding has hit all over China in recent days, killing more than 1,000 and leaving hundreds missing since the beginning of the rainy season.
Country-wide, the rains have caused at least $28bn in damage, and nearly 10 million people have had to be evacuated.
Soldiers reached the isolated town of Liangjiang on Saturday evening to help 10,000 residents evacuate, said Sun, of the Antu County.
Further downstream, soldiers, police and fire fighters continued to retrieve thousands of barrels full of explosive chemicals that were washed away by flood waters into the Songhua River.
"The flood is unprecedented. Its devastation is appalling"
Sun Jingyuan, official in the northeastern Antu County
Water supplies to the nearby city of Jilin were temporarily cut after the incident on Wednesday, leaving 4.3 million people dependent on bottled water.
A total of 7,000 barrels were washed into the river, with around half of them containing volatile chemicals.
Most of the barrels were recovered by Sunday evening, Xinhua said, after boats were chained together across the 500-metre-wide waterway to block them from going further downstream.
But officials in neighbouring Heilongjiang reported that the chemicals had already affected their water.
The barrels were being rapidly swept down the river, after the Fengman Dam floodgates opened on Friday afternoon. Experts feared the barrels could explode if they hit a dam further downstream.
Al Jazeera's Melissa Chan, reporting from Beijing, said more than 1,000 people are killed annually in China floods but that the current situation was worrisome because of unusually heavy rains.
"The worry this year has been on the dams and the reservoirs ... This year it's been so much extra rainfall, about 15 per cent more than usual.
"That complicates the situation because the reservoirs are getting full and the dams are nearing their maximum capacity."
Until now, torrential rains have mostly hit China's south, swelling the Yangtze River - the nation's longest waterway - and some of its tributaries to dangerous levels.