International aid has started trickling into Mozambique, Zimbabwe and Malawi to ease the humanitarian crisis created by Cyclone Idai.

Key points: The current death toll sits around 350, mostly in Mozambique and Zimbabwe, with some projections as high as 1,000

The current death toll sits around 350, mostly in Mozambique and Zimbabwe, with some projections as high as 1,000 Floodwaters are still rising as torrential rain continues to fall

Floodwaters are still rising as torrential rain continues to fall Relief is starting to arrive after initially being cut off by bad weather

More than 300 people are now known to have died when the storm hit, but there are fears the final toll will be much higher.

In the Mozambican port city of Beira, people were still clinging to trees and roofs amid the floods, waiting for rescue teams almost a week after the powerful storm first struck.

Cyclone Idai lashed Beira with winds of up to 170 kilometres per hour last Thursday, then moved inland to Zimbabwe and Malawi, flattening buildings and putting the lives of millions at risk.

Mozambique has begun three days of national mourning for more than 200 victims, while the death toll in neighbouring Zimbabwe rose to more than 100 from one of the most destructive storms to strike southern Africa in decades.

Zimbabwean officials say the death toll could be sitting at about 350. ( AP: Tsvangirayi Mukwazhi )

Mozambican President Filipe Nyusi said after flying over the affected region on Monday he expected the death toll to be more than 1,000.

Zimbabwean officials say they fear some 350 people may have died.

Floodwaters are still rising thanks to torrential rain, according to aid groups trying to get food, water and clothing to desperate survivors.

Floodwaters are still rising as rain continues to fall. ( IFRC via AP: Denis Onyodi )

In Zimbabwe officials said locals had told them the force of the floodwaters swept some victims down the mountainside into Mozambique.

Entire villages were swept away, said General Joe Muzvidziwa, who was leading the military's rescue efforts in Zimbabwe. Some people had been out at beer halls when the cyclone hit and came home to find nothing left.

In Beira, drone footage released by the Red Cross showed residents of a shantytown picking through wreckage and trying to drag plastic sheeting over their ruined homes. It also showed the settlement pockmarked with empty plots where whole buildings had been blown off their foundations.

AP/ABC