Subsidence in northern Thai Nguyen Province is being blamed on an underground karst funnel in the limestone bedrock that is 60m long and 30m wide, according to the Ministry of Natural Resources and Environment.

The ministry said that in Dai Tu District, there is a limestone cave 8-40m below the surface that has resulted in the formation of the karst funnel and subsequent subsidence on the surface.

Since the end of January, cracks measuring 1.5cm in diameter have appeared in Can village.

The village has also experienced land subsidence of between 15m-20m in width.

Nguyen Van Du, a local resident, said that a number of households have been forced to leave their homes.

Subsidence has also affected Nam Hoa and Cay Thi communes in Dong Hy district.

Duong Minh Thu, deputy chairman of Cay Thi commune's People's Committee, said that about 50 sites had been affected by land subsidence in Trai Cau village. The worst affected site has sunk 10m and measures 100m in diameter.

Deputy Prime Minister Hoang Trung Hai has asked the ministry to rectify the situation and identify the cause of the subsidence.

The provincial People's Committee has relocated households in the vicinity of the Karst funnel.

The ministry said that there was a high risk that surface cracks in Dai Tu district would spread to neighbouring areas and it asked local authorities to fence off the most dangerous localities in the district./.