Floods in Ougadougou have almost brought the city to a standstill
Heavy flooding has now affected some 350,000 people across West Africa, killing at least 30 in Ghana and Burkina Faso, UN officials say.
More than 100,000 people in Burkina Faso have fled their homes, mainly in the capital Ougadougou.
A UN spokeswoman said the amount of rain that fell in Ougadougou on one day this week was equal to a quarter of the whole country's annual rainfall.
Neighbouring countries affected include Benin, Guinea, Niger and Senegal.
Earlier in the week, Burkina Faso's main hospital was badly flooded and had to evacuate patients, some with infectious diseases.
At least seven people are known to have died from the floods in the country and President Blaise Compaore has appealed to the international community for help.
He said those made homeless were being temporarily re-housed in schools and colleges.
Prime Minister Tertius Zongo said on Friday the cost of flood damage had risen to $152m (£92m) and included two destroyed dams and 12 damaged bridges.
The authorities in Burkina Faso were forced to open the main gate of a hydroelectric dam in the Volta River basin near the Ghana border to prevent further flooding.
In Ghana at least 25 people have already died in flooding-related incidents, officials say.
Elisabeth Byrs, of the UN Office for the Co-ordination of Humanitarian Affairs in Geneva, said the death toll was likely to increase.