Severe floods caused by heavy rains have forced thousands of people to flee their homes in Mozambique and left some stranded on roofs as surging waters swamp settlements, officials and witnesses said on Monday.

President Daniel Chapo cancelled his trip to the World Economic Forum in Davos and said on social media late on Sunday that “the absolute priority at this moment is to save lives”.

Hospital worker Celeste Maria told she and her family fled their home in Chokwe in the southern province of Gaza after authorities sent out warnings about intensifying rains last week, according to Reuters.

“Our home is now completely submerged. We left behind neighbours who are now telling us they are sheltering on rooftops as the water continues to rise,” the 25-year-old said by phone from a resettlement centre.

Rising waters submerged trees, leaving only the top branches visible above the surface in photos shared by Gaza’s provincial council.

On Monday, it posted an alert that there was a crocodile in the public square in Xai-Xai, the provincial capital.

The southern African country has been hit by frequent weather-related disasters that scientists say have been exacerbated by climate change. Local media reports said the flooding could be the worst in two decades.

The most affected province was Gaza, just north of capital Maputo, the United Nations Office for the Coordination of Humanitarian Affairs said on Sunday, citing data from the national disaster agency.

More than 400,000 people have been impacted and more than 29,600 houses have been partially or completely destroyed in five affected provinces, it added.

There were no immediate estimates of the number of people killed or injured. Authorities say more than 100 people have died since the start of the rainy season in October.

A spokesperson for Maputo Port said operations were slower than usual but “did not stop”. Petrochemical company Sasol and logistics firm Grindrod said their operations have not been affected at this stage.

Neighbouring South Africa deployed an air force helicopter 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.