Torrential downpours since December have left large swathes of Mozambique underwater, affecting more than half a million people and claiming dozens of lives, with damage and losses also reported in neighbouring South Africa and Zimbabwe.

"Extreme 10-day rainfall events in the region have become significantly more intense due to human-induced climate change," researchers for the World Weather Attribution (WWA) network of scientists said in a report.

The international group assesses the role of climate change in extreme weather events.

Between January 10 and 19, areas of southern Mozambique -- including the severely affected Gaza province -- received upwards of 500 millimetres (20 inches) of rain, the report said.

This was equivalent to more than the usual rainfall for an entire year, it said.

"Human-induced climate change has increased the intensity of such extreme rainfall by about 40 percent," said climatologist Izidine Pinto from the Royal Netherlands Meteorological Institute.

"The combination of very intense rain over a short period, together with high vulnerability and exposure, led to the worst flooding in Mozambique in 25 years," Pinto said in a press briefing ahead of the report's launch.

The cooling weather phenomenon known as La Nina -- which tends to "produce above-normal rainfall conditions over Southern Africa" -- was in turn responsible for about 22 percent of the rainfall's intensity.

Nearly 140 people have died in Mozambique's floods since October 1, according to its National Disasters Management Institute (INGD), and some areas remain inaccessible by road after rivers burst their banks.

Floodwaters also claimed more than 30 lives in South Africa's Limpopo and Mpumalanga provinces, causing millions of dollars in damages including in the famed Kruger National Park.

The natural disaster was "a textbook case of climate injustice", said climate science professor Friederike Otto from London's Imperial College.

"The people of South Africa, Mozambique, Zimbabwe, and Eswatini have not contributed to climate change, nor are they profiting from using or selling fossil fuels," she said.

"Yet they are the ones losing their lives, homes and livelihoods."