Relentless rain has lashed south-central Vietnam since late October, and historic sites and popular coastal holiday destinations have been hit by several rounds of flooding.

At least 16 people have been killed since the weekend, while the search was ongoing for five others, the environment ministry said Thursday.

More than 43,000 houses were submerged while several major roads remained blocked due to landslides.

Rescuers using boats in central Gia Lai and Dak Lak provinces pried open windows and broke through roofs to assist residents stranded by the high water on Wednesday, state media said.

In coastal Nha Trang, a popular tourist destination known for its pristine beaches, whole city blocks were inundated and hundreds of cars were underwater on Thursday, AFP photos showed.

In highland passes around Da Lat, multiple deadly landslides have occurred, with some areas recording up to 600 millimetres (two feet) of rain since the weekend, according to the national weather bureau.

Emergency hotlines recorded unusually heavy call volumes on Wednesday night as water levels across the region rose, state media said, adding the defence ministry had deployed helicopters to search for stranded people.

Water levels in the Ba River in Dak Lak surpassed a 1993 record in two places early Thursday, while the Cai River in Khanh Hoa province also surged to a new high, according to the weather bureau.

The historic floods occurred as heavy rains added to already high water levels, Hoang Phuc Lam, deputy head of the National Center for Hydrometeorological Forecasting, said on state television.

Natural disasters have left 279 people dead or missing and caused more than $2 billion in damage from January through October, according to Vietnam's national statistics office.

The Southeast Asian nation is prone to heavy rain between June and September, but scientific evidence has identified a pattern of human-driven climate change making extreme weather more frequent and destructive.