Three days of national mourning began Wednesday in Mozambique after one of the most destructive storms to strike southern Africa in decades killed hundreds of people..

Cyclone Idai, packing sustained winds of up to 170 kilometers per hour, hit Mozambique’s port city of Beira last Thursday before sweeping inland to Zimbabwe and Malawi.

Forecasters predict more torrential rains are expected through Thursday and floodwaters are still rising. Aid groups are trying to transport essential goods to desperate survivors.

President Filipe Nyusi said Tuesday Idai had killed more than 200 people in Mozambique and that rescuers were still finding bodies. After flying over affected areas on Monday, Nyusi said he expected the death toll to exceed 1,000. The confirmed death toll Wednesday in Mozambique, Zimbabwe and Malawi stood at more than 300, officials said.

Aid agencies said they prepared for the cyclone but not for the massive floods that followed. Mozambique was hardest hit as a result of rivers flowing downstream from its neighbors. The agencies said they were struggling to reach many survivors stranded in badly damaged remote areas of Mozambique.

Mozambique and South Africa are conducting aerial rescue and aid distribution missions. The U.N. World Food Program said it was transporting enough aid for 600,000 people. The U.N. said it had allocated $20 million from its central emergency response fund, and it urged other donors to contribute. The European Union announced an initial aid package for the storm-stricken countries valued at nearly $4 million. Britain and the United Arab Emirates have also promised aid.

The U.S. State Department said the U.S. is supporting relief efforts “in coordination with our partners.”