Aid agencies have started appealing for funds to assist people hit by the floods in several African countries.
UN agencies are seeking $43m for Uganda, where the government declared an emergency after 50 people died.
The International Red Cross has sent relief experts to the continent to raise money and deal with emergencies in Ghana and Togo, as well as Uganda.
The UN says 1.5m people are affected by the floods which have hit countries from the east to the west of Africa.
Aid workers say food needs to be airlifted to areas which have lost their crops and are completely cut off.
The British Red Cross has launched an emergency appeal for flood-affected areas across the continent, saying it will work alongside the International Federation of Red Cross and Red Crescent Societies to "provide urgently needed relief, including shelter and water purification tablets, to those affected by the crisis".
The floods are said to be the worst in many countries for decades, with 250 killed and more than 600,000 displaced.
One area particularly badly affected is northern Ghana, where the White Volta River burst its banks following days of torrential rain and large areas of farmland were flooded.
The Ghanaian Navy is helping to get emergency supplies to villages cut off by the floods, but access is slowly improving as flood waters recede, BBC West Africa correspondent Will Ross reports.
There will however be a long-term need for food aid in many parts of northern Ghana, as the annual maize crop has been destroyed just before farmers were about to harvest, our correspondent says.
The Ghanaian government and humanitarian agencies have just ended a visit to the worst-hit areas.
In some parts of Uganda, access to villages is very difficult
But some villages remain cut off, only accessible by canoe - and all this just weeks after the same subsistence farmers were suffering from drought.
Officials in neighbouring Burkina Faso have denied accusations that they aggravated the flooding in Ghana by opening floodgates on a dam that lies upstream from the countries' common border.
Burkina Faso itself is also badly affected. Displaced people are sheltering in schools while waiting for the government to build makeshift shelters, the BBC's Pierre Kazoni reports.
In Uganda, the first priority is getting food to people whose crops have been destroyed by the flooding, the BBC's Sarah Grainger in Kampala says.
Already, the UN has diverted one helicopter from neighbouring Sudan's Darfur region and the WFP is requesting that two more be made available for the relief effort.
People who have lost their homes to the floods also need tarpaulins and tents and aid agencies are stressing that medical supplies will be important as the threat of water-borne diseases like cholera increases, she says.