Prolonged downpours caused by two tropical depressions have caused severe flooding across central Vietnamese provinces, leaving 18 people dead and 14 missing, the government said Monday, with yet another tropical storm looming.

"As of Sunday evening, a total of 15 deaths and 10 missing people were reported in provinces stretching along the central Vietnamese coastline and up into the central highlands," Vietnam's Central Committee for Natural Disaster Prevention and Control said in a report released on Monday.

Rough seas have sunk eight ships along the coast, including a cargo vessel that had 12 crew members on board authorities could only rescue 11 workers, one fell into the sea and drowned, his body found late on Sunday.

Two more people died at sea while four others remain missing in other incidents.

Local authorities have evacuated nearly 50,000 people to places of safety, the Committee said. The popular resort town of Hoi An is completely inundated, with all tourist activities ceased.

Central parts of the country have experienced heavy rains since Tuesday after an incoming cold spell combined with tropical turbulence.

Some locations received up to 1,200 millimetres of rain over the past week, the National Centre for Hydro-Meteorological Forecasting said.

Torrential rains have flooded more than 26,000 houses in the region, along with at least 70 schools. The relentless deluge has destroyed 382 houses and damaged 110,000 others.

Authorities have warned that more flash floods and landslides will occur in the coming days as the country is bracing for another incoming tropical depression, one that may grow into a tropical storm in the coming days.