An earthquake measuring 6.3 on the Richter scale hit northwest China's Qinghai Province at 9:22 AM on 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.

The quake was also clearly felt in the provincial capital Xining,

"We all jumped up in the middle of our morning editorial meeting," said Xinhua reporter Ma Yong based in Xining. The office is on the third floor of a four-storey building downtown.

The tremor was also felt in the industrial city Golmud -- the starting point of the world's highest railway, which goes to Tibet -- and Haixi prefecture's capital Delinha.

When the quake struck, many people ran out of buildings. "Some residents said it was the biggest tremor they felt since the 8.1-magnitude quake jolted Hol Xil in 2001", said Luo Zhenggang, an official in Golmud.

Hol Xil, a major nature reserve and habitat for the critically-endangered Tibetan antelopes, is in the Kunlun Mountain Range, near Golmud.

The Qinghai-Tibet railway seems largely unaffected by the earthquake. "Railway operation remains normal," said a company spokesman. "But we have tightened safety surveillance along the route, and equipped every train with additional mechanical engineers."

An earthquake measuring 6.6 on the Richter scale hit the same region in April 2003, but did not cause casualties, and only damaged old buildings.

The China Earthquake Administration suggested Monday's earthquake would have caused limited losses.

Just six months ago, on May 12, an 8.0-magnitude earthquake hit southwest China's Sichuan Province, leaving more than 80,000 dead or missing. It was the deadliest and strongest tremor to hit China since the 1976 Tangshan earthquake.

(Xinhua News Agency November 10, 2008)