LHASA, Nov. 20, 2017 -- Three people sustained minor injuries following a 6.9-magnitude earthquake that hit Nyingchi in southwest China's Tibet Autonomous Region at 6:34 a.m. Saturday.

The quake caused power failure and cracks in houses in a number of localities in Nyingchi City, according to the regional seismological bureau.

The epicenter was detected at 29.75 degrees north latitude and 95.02 degrees east longitude, according to the China Earthquake Networks Center. The quake struck at a depth of about 10 km.

The quake was felt strongly in several counties in Nyingchi. As of 6 p.m., 227 aftershocks had been detected, including one with a magnitude of 5or higher.

Basang Cering, Party chief in Zhaxigang Village of Lunang Township, told Xinhua that he could not stand still in his house when the quake struck. Six houses in his village were damaged by the jolt.

Sources with the regional power grid said the power grids of both Tibet and Nyingchi are operating normally, though it had launched an emergency response mechanism.

The China Seismological Bureau has launched a third-degree emergency response mechanism, and held a teleconference to monitor an investigation into the situation. A team of 32 experts has been sent to the quake zone.

The bureau observed that the highest seismic intensity of the quake affected an area of 500 square meters, which is sparsely populated.

The tremors triggered falling rocks, blocking a highway linking Nyingchi's city proper with Tangmai, one of the quake-hit townships. Armed police transport troops are clearing the road.

The Fire Department of the Ministry of Public Security said fire fighters from Nyingchi are ready in Tangmai Township. Another team of rescuers will take a helicopter to Gyalha village in the epicenter since the road to the village was blocked by rocks.

The Ministry of Transport has also dispatched staff to investigate the safety condition of bridges in the quake-hit area.

The Tibet subsidiaries of Chinese telecom providers China Mobile and China Tower said that their networks are operating normally. But the Tibet branch of China Telecom reported the disruption of an optical cable for broadband service in Pome and Zayul counties.