Authorities in the central Ha Tinh Province have evacuated residents living in a house where a sinkhole turned the backyard into two ponds last week.
Le Van Thuong of Huong Khe District said his family was watching televisio late at night on May 3 when they heard a gurgling sound, followed by a huge noise from the backyard like a truck loading off stones.
They rushed out and saw two ponds formed by the sinkhole in the previous land plot.
Each pond is around 8 meters in depth and 10 meters in diameter, with a layer of muddy water on the surface.
Thuong said several long cracks appeared around the ponds after that night.
Vo Ta Dinh, director of the provincial Department of Natural Resources and Environment, said the depression might have been caused by the activities of the karst topography in the region.
Karst typography is a type of landscape shaped by the dissolution of a layer or layers of soluble bedrock, and over time this forms most caves and caverns. However, sinkholes formed by this process can happen instantly.
The department has asked the provincial People's Committee to send scientists to survey the land plot to obtain more information.