Some 15,000 people still need to be rescued from the devastation caused by Cyclone Idai, Mozambique officials say.
The cyclone victims there are stranded by catastrophic flooding and are clinging to roofs or stuck in trees, charities say.
In the port city of Beira, aid workers say there are only two to three days of clean water left.
Some 300 people are confirmed dead in Mozambique and Zimbabwe, but the toll is expected to rise.
The powerful cyclone swept in to Beira last Thursday, with winds of more than 177km/h (106 mph). It left a trail of devastation as it moved inland.
Oxfam has told the BBC that an area of about 3,000 sq km (1,864 sq miles) is now under water.
Medical agencies are warning that the shortage of food and clean drinking water is increasing the threat of disease.
