(CNN) -- A rapid series of strong earthquakes hit a mountainous and impoverished area of China's Qinghai province early Wednesday, the U.S. Geological Survey said.
About 300 people were killed, state-run Xinhua News Agency reported, adding that another 8,000 have been injured.
Many others, including primary schoolchildren, were feared buried under debris after a 6.9-magnitude earthquake struck at 7:49 a.m. local time (7:49 p.m. ET Tuesday), when many people were probably still at home and schools were beginning the day.
The USGS also recorded three strong aftershocks -- of magnitudes 5.8, 5.2 and 5.3 -- all within two hours of the first quake.
"We have to mainly rely on our hands to clear away the debris as we have no large excavating machines," police officer Shi Huajie told Xinhua. "We have no medical equipment, either."
A Chinese military official told Xinhua that the death toll was expected to rise, given the damage to homes.
He said dispatched soldiers were setting up tents and transporting oxygen for the injured but affected roads leading to the airport could hamper relief efforts.
The Ministry of Civil Affairs plans to distribute 5,000 tents, 50,000 coats and 50,000 quilts to the earthquake zone, Xinhua said.
The epicenter was located in remote and rugged terrain, about 150 miles (240 kilometers) northwest of Qamdo, Tibet. Qinghai borders the autonomous regions of Tibet and Xingjiang and the provinces of Gansu and Sichuan.
Xinhua said the quake hit the prefecture of Yushu, a Tibetan region of Qinghai with about 80,000 people.
More than 85 percent of the houses in the county seat of Jiegu, had collapsed, a prefecture official told Xinhua.
"Many are buried in the collapsed houses, and there are still lots of others who are injured and being treated at local hospitals," he said.
Xinua said residents near the epicenter also reported casualties and collapsed buildings.
Karsum Nyima, deputy director of news at local Yushu TV, told Xinhua that most of the houses in the area were made of wood with earthen walls. He said some had come tumbling down, including a Buddhist pagoda in a park.
In 2008, 70,000 people died when a 7.9 earthquake rocked neighboring Sichuan province, northwest of its capital, Chengdu.