Yingjiang, a county in southwest China's Yunnan Province, is watching out for secondary disasters as students returned to school Monday, four days after a 5.8-magnitude earthquake jolted the county.

About 75 percent of the county's 31,141 primary and junior high school students went back to school Monday, the county's education chief Li Shaobo said.

He said 143 primary schools and 15 junior high schools reopened Monday, and the remaining five schools that were seriously damaged by the quake would resume classes next week.

Li said the education authority had closely examined all school buildings, and ensured adequate supplies of tents, food and quilts for boarders.

About 6,500 square meters of prefabricated housing had been set up on campus to replace rattled school buildings, he said.

The quake left 25 people dead and 314 injured in Yingjiang. It toppled 1,039 homes and seriously damaged 4,994 others.

Though the provincial earthquake administration has not forecasted more powerful quakes for the region, county authorities are on alert for secondary disasters, said Yang Mei, the county's land and resources chief.

Yang said his colleagues had observed a crack of 6-km along the banks of Dayingjiang River. "The widest part measures 20 cm and the deepest section measures 2 meters," he said.

Meanwhile, smaller crevices were observed in several villages near the epicenter, he said.

Secondary disasters were feared in at least five villages, where flowing sand and water were seen underneath homes and in cropland, said Yang.

He said the bureau had launched around-the-clock monitoring for landslides and mudrock flows.