Three million residents in the Chilean capital Santiago have been left without clean water after landslides caused by heavy rains polluted the rivers supplying the city.

Key points: Three million Santiago residents without clean drinking water

Three million Santiago residents without clean drinking water Major supply rivers polluted by landslides caused by heavy rains

Major supply rivers polluted by landslides caused by heavy rains More bad weather predicted over the weekend

The national emergency response agency declared a red alert in the city, home to more than 7 million people.

"Unfortunately the weather system over the metropolitan region brought rain that caused increased sediment in the Maipo River," Santiago Mayor Claudio Orrego told reporters.

He said that meant "a water cut for the population affecting about 3 million people".

The corporate manager of a local water supplier said production was down to 35 per cent of normal levels.

Heavy rains in the Andean foothills since Friday triggered landslides into the Maipo and Mapocho rivers.

Municipal authorities activated an emergency plan that includes tapping into 45 backup water sources and mobilizing more than 60 water trucks.

Images shared on social media showed bare shelves at supermarkets, where thousands flocked to stock up on bottled water.

In the O'Higgins region 90 kilometres south of Santiago, the swollen Tinguiririca River left one person missing and about 100 homes damaged.

Four municipalities in the region were also on red alert with rain expected to continue throughout the weekend.

AFP