The death toll in three south-eastern African countries -- Mozambique, Malawi and Zimbabwe -- has climbed to more than 400 people following cyclone Idai that triggered devastating floods.

Mozambique has declared a state of emergency and has appealed for international aid as thousands more people remain at risk with people clinging to roofs and trees, according to the latest media reports.

Addressing the media, Mozambique’s land and environment minister, Celso Correia, warned that the number of dead was rising as rescue and flood workers retrieved bodies that had been hidden in the now-receding flood waters.

"Our biggest fight is against the clock," said Correia from the flood-ravaged port city of Beira. The minister added that 15 000 people were still in need of help.

"They are alive, we are communicating with them, delivering food, but we need to rescue them and take them out."

Rescuers in the town of Buzi in Mozambique’s Sofala Province are now focusing on delivering aid and evacuating people. But rescue teams are battling to access thousands of survivors stranded on roofs and trees with more helicopters and boats needed to carry out rescues.

Aerial images released by Mozambique’s disaster relief agency, the INGC, showed survivors packed together on top of high buildings in Buzi district, which is the worst affected area.

In Zimbabwe, state broadcaster ZBC said the death toll had risen to 139, up from 100 on Wednesday, while the World Food Programme (WFP) said 200 000 Zimbabweans would need urgent food aid for three months.

In Malawi, 56 people were confirmed dead, and 82 000 people were displaced.

More than 400 sq kilometres in the region devastated by the flooding are under deep water, according to satellite images taken by the European Union (EU), and in some places the water is six metres deep.

At least 600 000 people have been affected, according to the UN Office for the Coordination of Humanitarian Affairs (OCHA), ranging from those whose lives are in immediate danger to those who need other kinds of aid, the Guardian reported.

And the floodwaters are predicted to rise in the coming days as heavy rain continues to fall in the effected region.