An earthquake measuring 6.3 on the Richter scale hit northwest China's Qinghai Province at 9:22 a.m. Monday, but as yet no casualties have been reported.

The epicenter was in the Mongolian-Tibetan Autonomous Prefecture of Haixi, at 37.6 degrees north latitude and 95.9 degrees east longitude, about 716 kilometers west of the provincial capital Xining, according to the National Seismic Network.

Exactly an hour after the quake, the Qinghai provincial seismic network monitored an aftershock measuring 3.9 in the same area.

The earthquake toppled several ramshackle huts in Da Qaidam district near the epicenter, and some other mud houses had cracks on their walls, said Gu Xiaodong, a deputy official of the administrative committee of the District.

"No casualties have been reported as yet," said Gu.

Schools in Da Qaidam have been closed for safety considerations and classes will be suspended for at least one day, he said.

A group of Xinhua reporters are driving to Da Qaidam as there's no flight to the nearest town, Golmud, on Monday. Their journey of about 700 kilometers on mountain roads will take until 10 p.m.

Da Qaidam is sparsely populated with about 16,000 people, including Mongolians, Tibetans, Muslim Hui and Han, according to the county government's website.

Da Qaidam, which literally means "a big salt lake" in the Mongolian dialect, is rich in mineral resources, with one of the largest lead-zinc mines in western China and several coal mines.

Gu said the epicenter was close to two coal mines, Kaiyuan and Dameigou. "But no serious damage has been incurred."

At least seven mines in Haixi prefecture, near the epicenter, reported they felt the tremor, but there are no reports of casualties.

More than 200 miners in Dameigou Coal Mine, about 15 kilometers from the epicenter, have been safely evacuated from underground after the quake. The quake caused cracks in the mine's administrative building and dining room.