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

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

Business owner Bui Quoc Vinh, 45, said he was safe in his 24th-floor apartment in Nha Trang but his restaurants and shops on the ground floor were under about a metre of water. His employees were even worse off.

"I am worried about our furniture in my restaurants and shops, but of course I cannot do anything now," he told AFP.

"My staff have to take care of their flooded homes," which he said were under two metres (six feet) of water. "I don't think the water is going to recede soon as the rain has not stopped."

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

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

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

- Cancelled tours -

There were also deadly landslides in highland passes around the Da Lat tourist hub, with some areas recording up to 600 millimetres (two feet) of rain since the weekend, according to the national weather bureau.

Hotel owner Vu Huu Son, 56, said landslides had blocked all but one road to the city.

"I don't think we have tourists now as they all left at the weekend before the rain and also cancelled their tours here," he told AFP.

The government-run Hanoi railway corporation announced the suspension of several train lines linking the north and south due to the flooding, state media said.

Emergency hotlines recorded unusually heavy call volumes on Wednesday night as water levels across the region rose, state media said.

The defence ministry also deployed helicopters to search for stranded people.

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

The 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 between January and 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.