SYDNEY (AFP) - Dozens of firefighters from Australia and New Zealand departed for the United States on Sunday to help crews battle deadly blazes that have scorched the country's drought-ravaged west.

Seventy-one firefighters, including 15 from New Zealand, were flying to the worst-hit state of Idaho and are also being deployed to the affected states of Washington, Montana, Oregon, Idaho and California, the Australian authorities said.

They will face challenging conditions that have already claimed the lives of three firefighters in Washington, with large blazes burning across nine other states covering some 526ha.

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"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."

Under an exchange programme, Australian firefighters have been sent to the US 11 times since 2000. A different contingent recently returned from Canada after fighting wildfires in the country's southwest.

Mr Rogers said the crews were expected to stay in the US for about a month, working up to 14 hours a day for 14 days straight before a two-day break and another 14-day deployment.

The firefighters will be involved in efforts on the frontline, in the air and be part of management teams.

"Their logistics skills will be in high demand, especially managing aircraft to fight fires and ferry supplies to remote locations," Mr Kevin O'Connor of New Zealand's National Rural Fire Authority said in a statement.

"They are likely to be working in rugged, mountainous terrain, which will make for a demanding deployment, especially in the very high temperatures gripping those states at the moment."

US President Barack Obama Friday declared a wildfire emergency in Washington, which will release federal funds to help relief efforts in the state.

Almost 30,000 American firefighters and support staff are battling the blazes, supported by personnel from Canada and the US military.