Mozambique's President Daniel Chapo has cancelled his trip to the World Economic Forum in Davos this week due to severe floods that have damaged infrastructure and affected hundreds of thousands of people in the Southern African country.

Chapo wrote in a post on Facebook late on Sunday that Mozambique "is going through a tough time ... (and) the absolute priority at this moment is to save lives".

Heavy rains since mid-December have caused widespread floods in Mozambique's Gaza, Maputo and Sofala provinces, with several river basins above alert levels, the United Nations Office for the Coordination of Humanitarian Affairs said in a report on Sunday.

The OCHA report said authorities estimated that more than 400 000 people had been affected, with numbers expected to rise as rains continue.

Neighbouring South Africa has deployed an air force helicopter to Mozambique to help with search-and-rescue efforts.

Heavy rains have also affected parts of South Africa, including the northeast where its renowned Kruger National Park is located. On Monday Kruger reopened to day visitors after being closed for several days.

Flooding has become more frequent and severe in southeastern Africa as climate change makes storms in the adjacent Indian Ocean more powerful.