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

Whole city blocks were inundated in coastal Nha Trang, a tourist spot 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 (3.2 feet) 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 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 41 people have been killed across six provinces since Sunday, while the search was continuing for nine others, the environment ministry said on Thursday.

More than 52,000 houses were flooded and nearly 62,000 people were evacuated from their homes, while several major roads remained blocked due to landslides. A million customers were left without electricity, the ministry said.

- 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, the national weather bureau said.

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.

A 100-metre section of the Mimosa Pass roadway was blocked after a landslide late on Wednesday, and two other routes were closed due to landslide risks, state outlet Tuoi Tre News said.

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.

Deputy Prime Minister Ho Quoc Dung told the leaders of three flood-affected provinces, Khanh Hoa, Dak Lak and Gia Lai, to mobilise the army, police and other security forces to "promptly relocate and evacuate people" to safe areas, according to a government statement.

Rescuers brought food and water to flooded hospitals in the coastal city of Quy Nhon in Binh Dinh province, state-run Thanh Nien newspaper said, after doctors and patients at one facility survived on instant noodles and water for three days.

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

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.

In Dak Lak, floodwaters swept 100 20-litre barrels of sulfuric acid from a sugar factory, the public security ministry said, warning the public to avoid the dangerous liquid.

Natural disasters have left 279 people dead or missing in Vietnam and caused more than $2 billion in damage between January and October, according to the 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.