Troops were helping the rescue efforts but the chances of survival for the five missing "is very low," said Ho Duc Phuoc, chairman of the provincial People's Committee, the local government.

"The search is very difficult because there are several huge rocks and we have had to mobilise soldiers to help," Phuoc said.

The accident happened when hundreds of tonnes of rock fell onto workers at Len Co quarry in Nghe An province, north central Vietnam, a district policeman told AFP, refusing to be named.

"Continuous rains over the past few days might have been the reason for the rockslide," he said, adding that hundreds of rescuers had joined the search for the remaining victims.

Five workers were freed from the rocks and rushed to local hospitals, Phuoc said.

Two of them had multiple injuries and broken bones, said a health official at the provincial hospital.

Deadly accidents frequently occur in quarries in the communist country where labour and safety regulations are often disregarded.

Agence France Presse- April 2, 2011