Aid workers are trying to rescue victims clinging to trees and crammed on rooftops against rapidly rising waters after a cyclone unleashed devastating floods in Mozambique, Zimbabwe and Malawi.

More than 238 people are dead, hundreds are missing and thousands more are at risk.

“This is the worst humanitarian crisis in Mozambique’s recent history,” said Jamie LeSueur, head of response efforts in Beira for the International Federation of Red Cross and Red Crescent Societies.

At least 400,000 people have been left homeless.

The rapidly rising floodwaters created “an inland ocean” in Mozambique, endangering tens of thousands of families, aid workers said as they scrambled to rescue survivors of Cyclone Idai and drop food, water and blankets.

President Filipe Nyusi said the death toll could reach 1,000.

Emergency workers called it the region’s most destructive flooding in 20 years. Heavy rain is expected to continue until Thursday.

“This is a major humanitarian emergency that is getting bigger by the hour,” said Herve Verhoosel of the World Food Programme.

Many people are “crammed on rooftops and elevated patches of land outside the port city of Beira” and WFP is rushing to rescue as many as possible, he said.

Mozambique’s Pungue and Buzi rivers overflowed, creating “inland oceans extending for miles and miles in all directions”, Mr Verhoosel said. Dams are at 95% to 100% capacity.

“People visible from the air may be the lucky ones and the top priority now is to rescue as many as possible,” he added.

The extent of the damage is not yet known as many areas remain impassible. With key roads washed away, aid groups are trying to get badly needed food, medicine and fuel into hard-hit Beira, a city of 500,000 people, by air and sea.

Queues for food supplies
Queues for food supplies (Tsvangirayi Mukwazhi/AP)

Cyclone Idai swept across central Mozambique before dropping huge amounts of rain in neighbouring Zimbabwe’s eastern mountains. That rain is now rushing back through Mozambique, further inundating the already flooded countryside.

“It’s dire,” Caroline Haga of the Red Cross told the Associated Press from Beira. “We did an aerial surveillance yesterday and saw people on rooftops and in tree branches. The waters are still rising and we are desperately trying to save as many as possible.”

Satellite images are helping the rescue teams target the most critical areas, she said. Rescue operations are based at Beira airport, one of the few places in the city with working communications.

The waters flooded an area of land more than 30 miles wide in central Mozambique, putting more than 100,000 people at risk, said aid group Save the Children.

“The assessment emerging from Mozambique today is chilling,” said Machiel Pouw, Save the Children’s response leader in Mozambique. “Thousands of children lived in areas completely engulfed by water. In many places, no roofs or tree tops are even visible above the floods.”

“The full horror, the full impact is only going to emerge over coming days,” Red Cross spokesman Matthew Cochrane told reporters in Geneva.

Torrential rain is still lashing the region on Tuesday, and Buzi town could be entirely submerged within 24 hours, the aid group said.

Hardest hit was Beira, where thousands of homes were destroyed.

The city and surrounding areas were without power and nearly all communication lines were destroyed. Beira’s main hospital was also badly damaged.

Large areas to the west of Beira have been severely flooded and water has completely covered homes, telegraph poles and trees, the Red Cross said.

The nearby cities of Dondo and Chimoio were also badly affected.

Residents dig for victims
Residents dig for victims (Tsvangirayi Mukwazhi/AP)

In Zimbabwe the death toll rose to 98, the government said.

The mountain town of Chimanimani was badly hit. Several roads leading into the town were cut off, with the only access by helicopter. Residents expected the death toll to rise.

President Emmerson Mnangagwa arrived in the area on Tuesday, saying a number of countries, including the United Arab Emirates, South Africa, Botswana, Namibia and Angola, were offering aid.

The US embassy in Zimbabwe said the US was “mobilising to provide support” to partners in the three affected countries, but provided no details. The European Union and Britain also pledged aid.

Malawi’s government confirmed 56 deaths, three missing and 577 injured, with 11,000 households displaced in the southern district of Nsanje.