"The numbers keep rising as extensive flooding continues and dams keep releasing water to avoid bursting," said Paola Emerson, head of Mozambique operations at the UN humanitarian agency OCHA.

Heavy rains and storms have battered Mozambique and neighbouring South Africa for weeks, claiming at least 150 lives, authorities in those countries have said.

"The situation remains fluid and dangerous," Emerson told a press conference in Geneva.

The damage to roads and infrastructure is making it hard for aid agencies to reach the worst-affected people, she said.

She was speaking from the city of Xai-Xai, around 200 kilometres (125 miles) northeast of the capital Maputo and in the Limpopo River basin.

Nearly 5,000 kilometres of roads had been damaged across nine provinces, including the main artery linking Maputo to the rest of the country, she said.

More than 50,000 people are sheltering in over 50 temporary accommodation centres.

The agency called for additional funding.

"This flooding emergency comes on top of massive conflict-related displacement in northern Mozambique that has depleted stocks," Emerson explained.

"This latest disaster is a stark reminder of Mozambique's vulnerability to the convergence of multiple shocks -- including conflict, drought, cyclones in recent years and now severe flooding."

- Crocodile threat -

Several rivers have burst their banks and swallowed entire neighbourhoods, raising risk of crocodiles entering communities, notably in Xai-Xai.

"The crocodiles that are in the Limpopo river, in this case, are able to get into... urban or populated areas that are now submerged under water," she said.

UN children's agency UNICEF said January's exceptionally heavy rains had "triggered a rapidly escalating emergency across vast swathes of Mozambique, particularly in the south".

"The flooding that we're seeing is not just destroying homes, schools, health centres and roads," said UNICEF spokesman Guy Taylor.

"It's really turning unsafe water, disease outbreaks and malnutrition into a deadly threat for children.

"The fact that Mozambique is now entering into its annual cyclone season creates the risk of a double crisis."

Taylor said disruption to food supplies and health services "threatens to push the most vulnerable children into a dangerous spiral".

"What happens in the coming days will really determine not only how many survive this emergency but how many can recover, how many can return to school and rebuild their futures," he said.