The fire was started by a lightening strike on Friday and has been gathering momentum over the weekend, rapidly devouring the dry forest amid exceptionally high temperatures and strong winds. Local officials said it has already covered 800-1000 acres.
An additional 130 firefighters and more water- and retardant-dropping aircraft were on their way to the site but officials expected the inferno would destroy around 250 homes in Yarnell - around half of the town.Hundreds of residents of Yarnell and Peeples Valley were being evacuated, officials said.
Arizona Senator Jeff Flake said he was in touch with local authorities, the White House and federal agencies "to ensure all resources are brought to bear".
He said he was "sick with the news" of the firefighting fatalities, which according to figures from the National Fire Protection Association constitute the largest loss of firefighter lives to a wildfire since 1933.
Sunday's deaths also mark the deadliest firefighting incident on US soil since the 9/11 attacks of 2001, when 340 firefighters were killed.