A 19th victim was buried in a house. Another person was seriously injured in the landslide, which occurred in an area ravaged by a deadly earthquake last month, the official Xinhua News Agency reported, citing a local education official.
About 2,000 local cadres, medics, police and military personnel were trying to rescue the victims, the Yiliang county government said on its website.
The landslide smothered the Tiantou Elementary School and hit two farmhouses in Zhenhe village around 8 a.m., it said. More than 800 people were relocated.
Rescuers rushed from the Yiliang county seat to Zhenhe three hours away to dig out the students, said Peng Hong, an official with the county foreign affairs office.
Peng said the cause of the landslide was not yet known, but Yiliang was struck by an earthquake last month that killed 81 people and devastated several villages. In addition, rain has lashed the region of mountains and sheer valleys.
Though Thursday was a holiday across China, students were in school to make up for days missed after the quake, Peng said.