The mountainous conditions in the US Pacific Northwest will be nothing new to the dozens of firefighters from Australia and New Zealand who have arrived to help battle the many blazes burning unchecked in the region.

``We're used to tall timber and steep territory," said Warren Heslip, a 47-year-old firefighter from Southland, New Zealand.

KEITH RIDLER / AP Warren Heslip, 47, of Southland, receives a yellow firefighting shirt at the National Interagency Fire Center in Boise, Idaho.

Heslip was among the 15 New Zealand and 54 Australian firefighters from the southern region picking up equipment on Monday (local time) at the National Interagency Fire Center in Boise, Idaho, before heading out to help a ground campaign led by firefighters from across the West and augmented by US soldiers.

The flames that claimed the lives of three firefighters in Washington state, injured four others and burned 200 homes also inspired an outpouring of volunteers who have been invited for the first time in Washington state history to help battle the blazes.

This summer's fire response across the West has been overwhelmed by destructive blazes tearing through the tinder-dry region.

DAVID RYDER The remains of waterfront homes on Lake Chelan destroyed by the Chelan Complex fire are seen in Chelan, Washington on Monday. The Australia and New Zealand firefighters will likely be sent to fight this "complex" of fires about 280 km east of Seattle.

The biggest fire burning Monday was in Washington's Okanogan County on the Canadian border, where a group of five fires raging out of control became the largest in state history, scorching more than 1036 square kilometres, fire spokesman Rick Isaacson said.

FROM THE ARCHIVES: US summons firefighters from New Zealand, Australia to battle blazes

Lightning-sparked fires broke the state record, surpassing blazes that destroyed more than 300 homes in the same county last year.

DAVID RYDER / REUTERS A sign of appreciation left by community members is pictured in an area affected by the Chelan Complex fire in Chelan, Washington on Monday.

"I'd like to set some different records," Okanogan County Sheriff Frank Rogers said.

The US is in the midst of one of its worst fire seasons on record with some 30,000 square kilometres scorched so far. It's only the sixth-worst going back to 1960, but it's the most acreage burned by this date in a decade, so the ranking is sure to rise.

So many fires are burning in the state that managers are taking extreme measures, summoning help from abroad and 200 US troops from a base in Tacoma in the first such use of active-duty soldiers in nine years.

DAVID RYDER / REUTERS Firefighters extinguish hot spots in an area burned by the Chelan Complex fire in Chelan, Washington on Monday.

Jim Whittington, a Bureau of Land Management spokesman in Portland, Oregon, said military assets cannot be used against wildfires until all civilian resources are deployed.

Since 1987, active duty military personnel have been mobilised to serve as wildland firefighters a total of 35 times. The last time was in 2006.

Since then, it has not been necessary to ask for military assistance until this fire season, Forest Service officials said.

DAVID RYDER / REUTERS The remains of a waterfront home destroyed by the Chelan Complex fire is seen in Chelan, Washington on Monday.

Nearly 4000 volunteers also answered the state's call for help, far more than will be accepted, said state Department of Natural Resources spokesman Joe Smillie.

The state is looking for former firefighters or heavy equipment operators who can bulldoze fire lines to corral the blazes and keep them from spreading in mountainous, timber-covered areas. So far, about 200 people with the right experience have been cleared to work.

The dozens of firefighters from Australia and New Zealand who arrived at the National Interagency Fire Center in Boise, Idaho, were being outfitted to fill a critical shortage of mid-level fire managers such as equipment bosses, strike team leaders and supervisors.

The Southern Hemisphere nations have been partners with the US for more than 50 years, able to lend out firefighters because the severest part of their fire seasons occur at opposite times of the year. The last time the US asked for their help was 2008, with 50 firefighters arriving. The US sent firefighters abroad in 2007.

Costs for the international firefighters will be paid by the agency they're assigned to, officials said, though no estimate was yet available.

Chris Arnol , international liaison for Australia and New Zealand firefighters, said at a news conference in Boise the firefighters were ready to assist.

``We understand how tough it is for you guys and we're happy to help," he said.

"We really appreciate the opportunity to come over here, not only to help you guys, but to look at home other fire authorities manage fire," Tim Mitchell, New Zealand fire liaison, told KTVB-TV.

The Aussies and Kiwis will get their assignments Tuesday (local time) but their main focus will likely be in Oregon and Washington, KTVB-TV reported.

Simon Martin, 40, a firefighter from Collie, Australia, was looking forward to helping..

``I'm sure there are a lot of fatigued firefighters out there," he said.