Four people have died in floods following days of incessant rains in southern Mozambique, the country's institute for risk management said on Saturday.

The National Institute for Disaster Management (INGD) said the deaths happened around the capital Maputo, while 14,000 people were evacuated out of more than 30,000 people estimated to have been affected by the flooding.

"We still have many people to rescue, (but) we are using small boats," INGD director Luisa Meque told a news conference.

"We think that if we had helicopters we would be in a better position to respond to the emergency, but we don't," she said.

The worst hit district is Boane, about 30 kilometres (18 miles) southeast of the oceanside capital Maputo.

Some 4,000 houses flooded as two bridges collapsed and several roads were completely submerged.

"Our houses are full of water, we don't have anywhere to sleep. Our barn went with the rain, we have no food," said Lurdes Simao Dove, after she was rescued from Boane district.

"People are being dragged with the water, there are a lot of houses... all are down with the water," she said.

With more rains forecast in the coming days, the flooding is expected to worsen.

"The forecasts show that this rain will continue to fall until Monday, (and) we think that the situation of the river basins is critical," said the department of water resources chief Agostinho Vilanculos.

He expressed fears that the main highway linking Maputo and the rest of the country in the north, risked being flooded.

Mozambique, which lies downstream of several major river basins, and experiences intense rainfall and tropical cyclones, is regularly hit by devastating floods