The death toll following Cyclone Idai in Mozambique could exceed the 1,000 predicted by the country’s president earlier this week, officials said.

The secretary-general of the International Federation of Red Cross and Red Crescent Societies in Mozambique, Elhadj As Sy, stressed the need for humanitarian assistance, and added: “We will be seeing more in the weeks and months ahead, and we should brace ourselves.”

The confirmed death toll in Zimbabwe, neighbouring Mozambique and Malawi surpassed 500 on Thursday, with hundreds more feared dead in areas that were completely submerged.

Mozambique’s president Filipe Nyusi warned earlier this week that as many as 1,000 people could be dead.

Thousands of people are making a grim voyage toward the city of Beira in Mozambique, which although heavily damaged is now a centre for rescue efforts.

Some walked along roads carved away by the raging waters while others were ferried by local fishermen. Helicopters set off into the rain for another day of efforts to find people clinging to rooftops and trees.

For those who reach Beira with their few remaining possessions, life is grim. Waterborne diseases are a growing concern. “The situation is simply horrendous,” Mr As Sy said after touring transit camps for the growing number of displaced.

“Three thousand people who are living in a school that has 15 classrooms and six - only six - toilets. You can imagine how much we are sitting on a water and sanitation ticking bomb.” Scots aid worker Ruaridh Waddell, who witnessed terrifying Cyclone Idai wreak its trail of destruction in Malawi, said that he expected its death toll to be much greater than originally predicted.

Aberdeen-born Mr Waddell, 37, watched from a mountain as devastating floods destroyed villages and homes across the African country’s disasterhit Shire Valley.

The Disasters Emergency Committee (DEC) has launched an urgent appeal for donations to help the people of Malawi, Mozambique and Zimbabwe.

The Department for International Development (DFID) has now pledged £20million worth of UK aid to support Cyclone Idai survivors in the African countries.

Mr Waddell – an aid worker with Canadian agency World Renew – said: “I was in Malawi when the cyclone hit.

“We’d actually gone away for a hiking weekend on the Thyolo mountains in southern Malawi. We’d heard there was going to be some bad weather, but we didn’t think it was going to be as bad as it was.

“We had incessant rain for five days. The Shire Valley was completely flooded. “Hiking in the hills above the Shire Valley, we could actually see all the flooding happen below. It was just water as far as the eye could see.”

The UK Government has announced £3.4m of aid will be used to immediately help give 65,000 Malawians emergency shelter and provide 150,000 people with food for two months.