The earthquake struck in the middle of the afternoon when classes and office towers were full.
The temblor was felt as far away as Pakistan, Vietnam and Thailand.
The official Xinhua News Agency reported that four of the dead were ninth-grade students killed when their high school collapsed. Photos showed heavy cranes trying to remove rubble from the ruined school. Xinhua did not say how many of the students were feared dead.
It said its reporters in Juyuan township, about 60 miles from the epicenter, saw buried teenagers struggling to break loose from underneath the rubble of the three-story building "while others were crying out for help."
Two girls were quoted by Xinhua as saying they escaped because they had "run faster than others."
The earthquake comes less than three months before the start of the Beijing Summer Olympics, when China hopes to use to showcase its rise in the world.
The earthquake struck in the middle of the afternoon when classes and office towers were full, about 60 miles northwest of Chengdu. There were several smaller aftershocks, the U.S. Geological Survey said on its Web site.
