A magnitude-6.6 earthquake struck China's Gansu province, in the country's north, at 7:45 a.m. on Monday morning (7:45 p.m. EDT Sunday), killing at least 75 people and injuring more than 400, state media reports.

The quake rocked Minxian County and Zhangxian County, both located near the city of Dingxi, and was followed by 411 aftershocks, including a strong magnitude-5.6 tremor, Xinhua news agency reports.

The China Earthquake Networks Center says the quake occurred at a depth of 20 km (12.4 miles), while Gansu's provincial earthquake administration says it was shallower and occurred at a depth of only 6 km (3.7 miles). The U.S. Geological Survey says the initial quake measured magnitude-5.9 and occurred at a depth of 10 km (6 miles).

Chang Zhengguo, spokesman for the provincial government, said at a press conference in the provincial capital of Lanzhou that the quake caused the collapse of more than 1,200 houses and inflicted severe damage to 21,000 buildings, Xinhua reports.

Residents of quake-hit areas told Xinhua that most of the victims were elderly people and children who failed to escape from collapsing buildings.

Power and communication have been disrupted in Zhangxian and Minxian counties following the quake, which occurred at a fault zone in the province. The region has registered 25 earthquakes with a magnitude of more than 5.0 in the past, according to Xinhua.

Authorities have deployed police, firefighters and paramilitary forces to assist in rescue and relief efforts, which could be hampered by heavy rains that are predicted in the area later this week and can be expected to cause landslides.

Gansu is a sparsely populated province, although the city of Dingxi, which lies about 1,000 miles southwest of Beijing, has a total population of approximately 2.7 million people.

In 2008, China’s southwestern province of Sichuan was jolted by one of the worst earthquakes in the nation’s history, resulting in the loss of 90,000 human lives.