Three construction workers aged 18-45 were killed and a fourth injured after a section of the wall they had been sleeping next to collapsed on them, the Tuoi Tre newspaper cited local authorities as saying.

Heavy rains, which battered the province's Thai Nguyen and Song Cong towns on Monday night and Tuesday morning, also flooded nearly 1,100 houses, 670 hectares (1,660 acres) of paddy fields and a local electricity substation, resulting in a power outage for the whole area, according to the Vietnam News Agency.

The rains also forced 307 schools to allow students to stay at home.

"Some schools are still operating normally but not all of their students come to class. Others have had walls knocked down or their yards and gardens flooded," said Nguyen Duc Thinh, deputy director of the province's Department of Education and Training.

While the rains have stopped since and the floodwaters have been drained, the department has instructed affected schools to continue allowing students to stay at home on safety considerations.

The province's Thai Nguyen Town was the most affected by the heavy rains, with 120 out of 145 schools having to close on Monday. The Thai Nguyen University of Education has also had to postpone the opening of its new academic year, scheduled for Monday.

According to the National Center for Hydro-Meteorological Forecasting, due to the effects of a trough forming over the southern area of the Red River Delta, Vietnam's northern provinces have had rains and thunderstorms since Monday. Thai Nguyen was among provinces that received rainfall of between 70-120 mm per day. In some areas the rainfall was as high as 150 mm.

The rains are forecast to last until Thursday.

Last year, natural disasters, mostly floods, storms and landslides, killed 181 people and left 37 others missing and caused losses of around VND20 trillion ($858 million).