The death toll has climbed to 89, with 5 others still unaccounted for, in an earthquake that hit northwest China's Gansu Province Monday morning, local authorities said.

As of 6 pm on Monday, 87 people in the city of Dingxi and two in the neighboring city of Longnan had been confirmed killed in a 6.6-magnitude quake that jolted the border of Minxian and Zhangxian counties at 7:45 am, the Dingxi municipal government said.

Minxian reported the bulk of the casualties, with 87 deaths, 5 missing and 515 injured, including 60 people in serious condition.

As of 6 pm Monday, 422 aftershocks had been recorded in the quake-hit region, with the strongest measuring 5.6 in magnitude, Chang Zhengguo, spokesman for the provincial government, said at a press conference held in the provincial capital of Lanzhou.

An initial investigation showed that the quake had caused the collapse of more than 1,200 houses and severely damaged another 21,000 homes, he added.

Two helicopters and about 3,000 armed police, firefighters, local militiamen and local government staff have been sent to the quake-hit region to help with rescue efforts.

Xinhua reporters who arrived at villages in Meichuan Township in Minxian said many rural buildings had been reduced to ruins and others had cracks in the walls.

Zhu Wenqing, a 40-year-old farmer from Meichuan's village of Majiagou, said his house survived the initial quake but eventually collapsed following seven or eight aftershocks.

Villagers said the victims were mainly elderly and children.

In Meichuan's village of Yongguang, the quake toppled wood and earthen structures and unleashed a landslide that buried 12 residents.

Two bodies have been found and one person has been pulled out alive, but rescue efforts have been slow due to a lack of heavy digging machinery, rescuers said.

Chu Xiaoyi, a 20-year-old villager, said the landslide completely destroyed his house. His family of three narrowly escaped by holding on to a utility pole.

"We were sleeping when it happened, so we ran out almost naked. Now we have nothing left and even our clothes are borrowed from neighbors," Chu said.

Many residents in Yongguan said they are concerned about the lack of food, shelter, electricity and unstable mobile phone signals after the quake damaged the county's infrastructure.

Communication in many villages in Meichuan and in 13 townships in Zhangxian has been cut off. Power has been cut off in five towns in the eastern part of Minxian.

The epicenter of the quake was monitored at 34.5 degrees north latitude and 104.2 degrees east longitude, the China Earthquake Networks Center said.

The earthquake happened in a fault zone that has seen 25 earthquakes with a magnitude of 5.0 or greater throughout history, the China Earthquake Administration said.

The strongest quake recorded in the fault zone had a magnitude of 8.0 and occurred on July 21, 1654. That quake happened about 121 km from the site of the latest quake, the administration said.

Locals in Minxian said the quake lasted for about one minute. The county government said most of its townships have been affected by the quake.

Wang Sanyun, secretary of the Gansu provincial committee of the Communist Party of China (CPC), and Liu Weiping, governor of Gansu, have arrived at Meichuan to oversee rescue efforts.

The Lanzhou Railway Bureau has initiated an emergency response to guarantee the safety of railway bridges and communication facilities in the province.

Light to heavy rain has been forecast in Dingxi, according to the provincial meteorological station. The rain will likely affect rescue efforts.

The earthquake was also felt in Gansu's cities of Tianshui and Lanzhou, as well as the cities of Xi'an, Baoji and Xianyang in neighboring Shaanxi Province.