The confirmed death toll from massive floods in the US state of Colorado was revised down Tuesday from eight to six, authorities said.

The Colorado Office of Emergency Management (COEM) said two people who had been presumed dead had now been listed as missing instead, "to more accurately reflect their status."

A second day of clearer weather helped emergency crews gain access to areas left devastated by a week of torrential rain which damaged roads, cut towns off from services and supply routes and forced thousands to evacuate.

The number of people unaccounted for was put at around 580 on Tuesday, though officials say that mostly means that people have been unable to contact authorities, rather than implying they might be dead.

Rain began pelting the western state early last week, with Boulder especially hard hit, seeing 7.2 inches (18.3 centimeters) of precipitation in about 15 hours starting Wednesday night.

Flash floods afflicted 17 counties down a 200-mile (320-kilometer) north-south section of the Front Range, where the Rocky Mountains meet the Great Plains, the COEM said.

In all 11,750 people have been evacuated. More than 17,000 residential structures have been damaged, and over 1,500 destroyed.