State media showed pictures of the inundated school in Heilongjiang province and diagrams of how some children struggled at windows amid floating books and bits of paper to escape water two metres (six and a half feet) deep.
Friday's mountain torrent, said to be the worst to hit the area in 200 years, was caused by two days of heavy rain, killing 88 pupils and four villagers, Xinhua news agency said. Seventeen people were missing.
Residents said the death toll could be as high as 200.
Classes started anew on Monday, but the Beijing News said of the 352 children originally at the school, only 125 were in class in the morning.
A photograph on the front page of the Beijing News showed the muddy hand prints slipping below the water line on a classroom wall in the sprawling, one-storey building.
The playground at the Shalan Central Primary School was covered in thick mud after the waters receded.
"Chairs, schoolbags, books and paper lay scattered in the mud. In the drab surroundings, a pink Mickey Mouse bag stood out," the China Daily said.
In a classroom where about 50 first-graders, aged about six and seven, were reportedly killed, the desks were piled up against the wall with broken chairs strewn over the floor.
Sha Xianjing, who teaches Chinese, had the presence of mind to guide more than 20 of her pupils, aged about 10, to safety, state media said.
Pushing the classroom door closed to stop water flooding in, Sha yelled for everyone to stand on their desks.
"Those near windows stand on the window sills. Those in the middle hold on to anything you can. Don't move! ... Don't be afraid! Hang on tight!" the China Daily quoted her as saying.
Sha broke the classroom windows with her elbows and swept away the broken glass with bleeding hands so that the children had something to hold on to.
Throughout the ordeal, she implored the children not to cry.
Wang Tongtang, an official from the Mudanjiang city government told a press conference on Monday evening that villagers had complained about not being able to get through to the police or local government during the flood.
The head of the local police station and head of the Shalan township's Communist Party branch had been detained and were under investigation following the tragedy, the Beijing News quoted an official from the area as saying.
Zhang Zuoji, governor of Heilongjiang province, would ask for "administrative penalties" in the wake of the disaster, Xinhua news agency said on Tuesday.
"Zhang said he felt very sad to see so many children killed and should bear unshirkable responsibility as the governor," it said.
- Reuters - Thomson Reuters Foundation
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