Cyclone Idai, "an uncommonly fierce and prolonged storm," was one of the worst storms to hit Africa, UN Secretary-General Antonio Guterres said on Tuesday.

"Mozambique, Zimbabwe and Malawi have suffered one of the worst weather-related catastrophes in the history of Africa," he said in a plea to countries to donate to a 281.7-million-U.S.-dollar flash appeal.

"The death toll across the three countries is at least 700, but with hundreds still missing," said the UN chief. "The devastation has affected an estimated three million people, nearly two-thirds of them in Mozambique."

"In an already intense storm season, Tropical Cyclone Idai delivered a direct, one-two punch of wind and flooding across a vast area long experiencing poverty and drought," Guterres said.

The UN chief pointed out the images emerging from the aftermath were "raging waters; people stranded on rooftops; schools, hospitals and homes in ruins; an entire city Beira practically was razed to the ground; and enormous expanses of farmland, which is Mozambique's breadbasket, were inundated on the eve of the next harvest."

"This year's harvest is lost in large parts of the country, and of course it will take a lot of time to fully re-establish working conditions for agriculture," he said. "The infrastructure that was destroyed, the houses, the cities, the equipment that was destroyed in a country that is extremely poor, as we know, this obviously will take time to rebuild."

"That is one reason more to accelerate our efforts," Guterres said. "That is one reason more for the international community to step up its support."