Australian and New Zealand firefighters have flown to the United States to battle massive wildfires raging across the drought-plagued Western parts of the country.

Seventy-one firefighters, including 15 from New Zealand, left their countries on Sunday for the worst-hit state of Idaho with 17 large fires as well as other affected states including Washington, Montana, Oregon and California.

The fires continued to grow on Saturday, prompting mass evacuations of local residents, with authorities scrambling to beat back the flames.

The blazes have claimed the lives of at least three firefighters in Washington in conditions which are hazardous for foreign firefighters.

"They've had a lot of different fires burning, so trying to get containment on some of the fires... that's going to be the key," New South Wales state's Rural Fire Service deputy commissioner Rob Rogers told AFP.

"Our firefighters are a mixture of people who have been there before and new people, so it will be challenging for them but we are confident they will be well-enough trained to deal with those challenges," he added.

The US federal government has declared a state of emergency in Washington with state officials desperately seeking volunteers to help fight the flames.

In northern Idaho, officials have evacuated residents as raging wildfires have already burnt down 42 homes.

On Saturday, strong winds blew smoke from the blazes in eastern Oregon and Washington across the Cascade mountain range.

At least 70 large wildfires have been raging since last week through several dry Western states, destroying more than 100 homes and dozens of outbuildings.