The 6.2-magnitude earthquake in Gansu province triggered sand boils in two villages of neighboring Qinghai province on Tuesday, with several villagers reported missing, according to Xinhua News Agency.

The sand boils occurred in the villages of Jintian and Caotan in Minhe county, Haidong of Qinghai province, resulting in a substantial number of homes being engulfed and washed away by mud.

According to Xinhua, as of 5:30 am on Wednesday, nine people from two households in Jintian were yet to be found.

Rescue efforts are ongoing. Wang Lyu, deputy head of the Qinghai team of China's National Fire and Rescue Administration, told Xinhua that 157 rescuers were busy working in the region, with many digging in the mud using spades and shovels because large excavation machines couldn't reach the rescue sites.

Han Yanyan, a senior engineer from the China Earthquake Networks Center, said that the natural phenomenon is the result of the fairly large earthquake that shook the area and does not necessarily indicate that any aftershock could follow.

Following a strong earthquake, the seismic activity in the Earth's crust causes a phenomenon called liquefaction in the deep layers of sandy soil containing water. This liquefied sand layer could reach the surface directly under pressure, resulting in sand boils, Han added.