Twenty people have died and four people remain missing in Saudi Arabia after heavy downpours triggered flash floods in the desert kingdom for nearly a week, the civil defence authorities said on Thursday.

People have drowned in several areas of Saudi Arabia, according to a statement by the civil defence quoted by SPA state news agency.

Rescue teams evacuated six villages in the southwestern Bisha province after a sand dam at the valley of Tabala partially collapsed, it said.

Authorities have been urging people to avoid wadi valleys and plains flooded by heavy rainfall which has continued since last Friday.

The vast Arabian Peninsula country has not experienced such a high volume of rainfall for 25 years.

But around 10 people were killed in 2011 when flooding swept through the western city of Jeddah, where 123 people also perished in floods in 2009.

The inability of Jeddah's infrastructure to drain off flood waters and uncontrolled construction in and around the city were blamed at the time for the high number of victims.