Nearly 10 million Americans have been warned to brace for potentially life-threatening flooding as dramatic scenes in Arizona showed motorists being plucked from raging waters.

Tucson firefighters raced to three swift-water emergencies in less than half an hour on Wednesday evening as muddy floodwaters surged through streets and washes.  The dramatic rescues offered an early glimpse of the danger facing the Southwest as a potentially historic deluge threatens Arizona, New Mexico, Utah and parts of Colorado. The National Weather Service has issued widespread flood watches across the region, while forecasters warn that exceptionally intense downpours could unleash dangerous flash flooding within minutes.