President Barack Obama signed a federal declaration of emergency for Washington State on Friday, authorizing the U.S. Department of Homeland Security and the Federal Emergency Management Agency to coordinate relief efforts in 11 counties and several American Indian reservations hard hit by wildfires.

Authorities late on Thursday ordered the population of Tonasket, a riverfront hamlet of about 1,000 residents just 25 miles south of the Canadian border, to flee their homes as flames closed in.

About 25 miles farther south along the same river, emergency officials early on Friday issued additional evacuation orders for parts of Okanogan, a larger town at the western edge of the Colville Indian Reservation, urging evacuees in a Facebook posting "not to wait for door-to-door notification."

Both communities were in the path of flames from a cluster of wildfires dubbed the Okanogan Complex, which has doubled in size since Thursday to scorch some 161,000 acres of brush and dry timber about 115 miles northeast of Seattle.

The Okanogan Complex includes the so-called Twisp River fire, which forced the evacuation of some 4,000 households in the towns of Twisp and Winthrop about 30 miles west of Okanogan in the foothills of the Cascades.

Further evacuations were ordered on Friday around Nespelem, a tiny settlement in the interior of the Colville Reservation, where homes and businesses were threatened by a separate blaze that has blackened some 88,000 acres of tribal lands.

At least 70 large wildfires have been raging since last week through several bone-dry Western states, the bulk of them in Washington, Oregon, Idaho, California and Montana, the National Interagency Fire Center in Boise reported.

More than 100 homes and dozens of outbuildings have been lost, but only one civilian death has been reported in the latest rash of fires: a 70-year-old woman who slipped and fell as she was securing her backyard chickens before fleeing her Idaho home last weekend.

Smoke and soot carried hundreds of miles by prevailing winds from the Northwest to the Rockies settled over parts of Colorado, prompting a "wildfire smoke health advisory" that urged elderly residents, young children and people with respiratory ailments to stay indoors.

The advisory was posted on Friday for Denver and the entire the northern tier of Colorado, from the Utah line to the Kansas border.

The Western blazes, under attack by more than 30,000 firefighters and support personnel, have collectively charred more than 1 million acres of landscape in the midst of frequent dry-lightning strikes and a heat wave gripping the region.

With manpower and other resources stretched thin, fire managers have turned to the U.S. Army, the National Guard and even personnel from Canada, Australia and New Zealand to furnish reinforcements.

So far this year, U.S. wildland blazes have claimed the lives of at least 13 firefighters, four more than died in the line of duty during all of 2014, the fire center said.

Three U.S. Forest Service firefighters in an engine crew died on Wednesday while battling what authorities called a “hell storm” of flames in Twisp.

Each of their bodies were removed from the scene Thursday in an individual ambulance, escorted by more than a dozen fire and police vehicles with lights flashing. Firefighters along the route saluted by holding their helmets over their hearts.

The dead were Thomas Zbyszewski, a 20-year-old physics major and actor at Whitman College in southeastern Washington; Andrew Zajac, 26, and Richard Wheeler, 31. “These are three big heroes protecting small towns,” Washington State Gov. Jay Inslee was reported as saying in The Seattle Times newspaper Thursday.

Al Jazeera and wire services