The death toll from flooding in Malawi has more than tripled with 176 dead and at least 200,000 displaced, the government says.
Vice president Saulos Chilima said dozens of people are still missing, with at least 153 unaccounted for in the worst affected southern parts of the country.
Speaking at a press conference in Malawi's commercial capital Blantyre, Mr Chilima said a joint operation between police and the army was under way to rescue hundreds who were trapped in their villages.
President Peter Mutharika has declared 15 of the country's 28 districts disaster areas.
Mr Chilima has asked for international assistance.
Mr Chilima said: "It's a very bad situation.
"I flew over some parts of the Lower Shire but we could not find anywhere to land," he said of the southern parts of the country. "It's a big challenge we have before us."
The United Nations World Food Programme said it plans to airlift more than 100 metric tons of food to the southern African nation to feed at least 77,000 people.
Tents have been set up for those left homeless, and many have found refuge with friends and neighbours whose homes survived, according to aid organisation Doctors Without Borders.
"The floods are behaving like a slow tsunami with the river swelling progressively downstream toward the south and Mozambique," said Amaury Gregoire, Doctors Without Borders' mission head in Malawi.
The international medical organisation said it was concerned that displaced people were also vulnerable to water-borne disease due unsanitary conditions.
In neighbouring Mozambique, at least 38 people have died during heavy flooding, according to Mozambican news agency AIM.
The Zambezia province has been the worst affected, where the Licungo river has reached its highest levels since 1971, leaving thousands homeless.