The heaviest flooding to hit Ecuador in two decades has killed at least 18 people in Quito, washing away cars, damaging homes and sweeping away volleyball players and spectators on a sports field, officials said Tuesday.

Sixteen people have been reported missing and 46 injured, six of them critically, Ecuador's SNGRE emergency service said on Twitter.

Video footage shows torrents of water carrying stones, mud and debris down streets in the Ecuadoran capital as rescuers help inhabitants wade through the fast-running currents to safety.

Many were brought to shelters. 

The deluge damaged roads, agricultural areas, clinics, and schools.

Rescuer Cristian Rivera said many people had to be treated for hypothermia after wading through mud that reached to their knees.

Quito mayor Santiago Guarderas said a torrential downpour had overwhelmed a hillside water catchment structure, sending a kilometer-long deluge through a sports field where volleyball players were practicing as spectators looked on.

It was not immediately known how many of them were among the victims.

The Quito municipality has mobilized with heavy machinery to clear roads and fix the failed water catchment system.

Power was lost in the affected parts of the city after electrical poles were brought down by the deluge.

Dozens of soldiers were deployed to assist in search and rescue efforts of the police and fire brigades.

The flood began on the slopes of the Pichincha volcano which overlooks the nation's capital. 

Guarderas said Monday's rainfall brought down 75 liters per square meter following 3.5 liters on Saturday.

This is "a record figure, which we have not had since 2003," he added.

Heavy rains have hit 22 of Ecuador's 24 provinces since October, leaving at least 18 dead and 24 injured as of Sunday, according to the National Risk Management Service.

Scientists say climate change is intensifying the risk of heavy rain around the world because a warmer atmosphere holds more water.