Dozens have been rescued and sent to hospital, while many more bodies have been brought out and lined up under makeshift tarpaulin covers.
Mourners lit incense and candles around the bodies or let off fireworks in a traditional ritual to ward off evil spirits.
Rescuers told the official Xinhua news agency that they could still hear some buried students calling for help.
Al Jazeera correspondent Melissa Chan who is near the school said heavy cranes and other lifting equipment was being brought to the scene.
But she said the effort to care for survivors was being complicated by a lack of power and the fact that the nearest hospital had itself collapsed in the quake.
Thousands of children across the region were in class when the earthquake struck on Monday afternoon.
|Parents face an anxious search for |
missing sons and daughters [EPA]
A lucky few escaped unscathed because they were having sports lessons or exercising outside when the quake hit.
Students were also reported to be buried under collapsed buildings in at least five other nearby schools.
In Beichuan county another 1,000 students and teachers were reported either killed or buried after their six-to-seven storey school building collapsed.
"I just pray my child is safe and sound," one crying mother told Xinhua.
The agency said many parents burst into tears when a rescuer pulled out one girl who had lost her legs.
A teacher at the Juyuan school who only gave her surname as Cai said most of the teachers and students in 24 classes were buried in the rubble after the six-storey building collapsed.
Cai said the building housed classes for secondary two and three students.
Al Jazeera's Melissa Chan, reporting from the scene, said the entire middle of the school had caved in and disappeared into a gaping hole.
Wen Jiabao, the Chinese premier, visited the school on Monday night and offered hope to parents who were waiting in the rain for the news of their children.
"Some of the trapped still have chance to survive and we will go all out to rescue them," he said.
Two female students who survived the collapse told China's Xinhua news agency they had escaped because they had "run faster than others".
"Some had jumped out of the window and a few others ran down the stairs that did not collapse," said a villager who lived close to the school.
Schools and kindergartens in affected areas across Sichuan province were ordered to close on Tuesday until further notice.