The UN Office for the Coordination of Humanitarian Affairs said at least 20 people died as heavy rains and flooding over the past few days swept away their homes and cars in Afghanistan's southern Kandahar province.

Widespread flooding inundated Kandahar city and surrounding districts, with 97mm of rain falling in affected areas, the UN agency reported.

Kandahar's deputy governor Abdul Hanan Moneeb said the flooding was the worst in at least seven years, with many nomadic herders camped in the area swept away by the floodwaters along with their livestock.

The official added that 400 families have been rescued by the Afghan army since the flooding began late Friday night.

Rescue operations, however, were largely delayed due to heavy rainfall, Raziq Shirzai, the provincial commander of the Afghan air force, told AFP.

Heavy snowfall across large swathes of Afghanistan this winter has raised fears of severe flooding as spring approaches, following years of devastating drought in the country.