At least 23 people had been injured in the 5.1-magnitude earthquake that hit southwest China's Yunnan Province Thursday, local authorities said.

All of them were slightly injured. Fifteen of them were from Lufeng while eight came from Yuanmou, two neighboring counties. Many houses were toppled, said Zhang Jianguo, head of Yunnan's Earthquake Research Institute.

The earthquake struck at 12:56 p.m. in the area between Lufeng and Yuanmou. Its epicenter was located at 25.4 degrees north latitude and 101.9 degrees east longitude, at a depth of 16 km, according to China Earthquake Administration.

Lufeng is known as China's largest source of dinosaur bones. Anthropoid at Lufeng dated back to eight million years ago. Homo Sapian fossils in Yuanmou, or homo erectus yuanmouensis, dated back to some 1.7 million years ago.

No damages to the heritage sites have been reported as of Thursday night.

Yunnan's seismological bureau have detected 14 aftershocks of the quake with a highest magnitude of 2.9, said Gu Yishan, an official with the bureau.

Rescue work is going on, Gu added.

Earthquakes measuring 5 degrees or above on the Richter scale frequently hit the region in history, said Gu.