Cracks measuring dozens of meters in Binh My Commune in An Giang Province’s Chau Phu District are now advancing towards more residential areas, authorities said.

11 families had been evacuated before the collapse. Personnel have been stationed to monitor the section and warn the public if required.

An investigation found that the erosion had occurred because of whirlpools caused by the topography of the Hau River’s bottom at the spot, authorities said. The Hau River is one of the two tributarites of the Mekong in Vietnam.

The highway had been reinforced with sand bags at a cost of around VND25 billion ($1.07 million) after an 85 m section fell into the water on August 1, but 90 percent of them slipped into the river on Sunday.

The work had not been done properly, Nguyen Viet Tri, Director of the An Giang Department of Transport, said.

The cost of repairs and reinforcement now would be borne by the original contractor, My Luong Construction, Commerce and Service firm.

But the process has been temporarily halted by An Giang authorities pending consideration to choose the best option.

Around 100,000 families in the country live in areas vulnerable to erosion and landslides, Tran Quang Hoai, head of the Vietnam Disaster Management Authority, said while on a visit Tuesday to Sa Na village in Quan Son District, the central province of Thanh Hoa, where seven people died due to flooding earlier this month.

The construction of facilities to manage disasters, especially in mountainous areas, needs to be carefully considered, he warned.

Hoai's agency is set to appraise the government about which areas and households are vulnerable to erosion and put up signboards to warn people in dangerous areas, he added.

The 142-kilometer National Highway 91 runs from Can Tho City to the Cambodian border in An Giang.

In the Mekong Delta, Vietnam's food basket, a total length of 786 kilometers face the threat of erosion at 562 riverine and coastal points.

It is losing 500 hectares of land to erosion every year, and this is expected to directly impact the lives of one million people by 2050, according to the Ministry of Agriculture and Rural Development.

Fingers have been pointed at overexploitation of groundwater and sand mining as the cause.