BLY, Ore. — Out-of-state crews headed to Montana on Saturday to battle a blaze that injured five firefighters as the U.S. West struggled with a series of fires that have ravaged rural lands and destroyed homes.

Progress was being made on the nation’s largest blaze, the Bootleg Fire in Oregon, but less than half of it was contained, fire officials said. The growth of the sprawling fire had slowed, but increased fire activity was expected Saturday, and thousands of homes remained threatened on its eastern side, authorities said.

“This fire is resistant to stopping at dozer lines,” Jim Hanson, fire behavior analyst, said Saturday in a news release from the Oregon Department of Forestry. “With the critically dry weather and fuels we are experiencing, firefighters are having to constantly reevaluate their control lines and look for contingency options.”

In California, Gov. Gavin Newsom on Friday declared a state of emergency for four northern counties because of wildfires that he said were causing “conditions of extreme peril to the safety of persons and property.” The proclamation opens the way for more state support.

On Saturday, fire crews from California and Utah were headed to Montana, Gov. Greg Gianforte announced. Five firefighters were injured Thursday when winds blew flames back on them as they worked on the Devil’s Creek fire burning in rough, steep terrain near the rural town of Jordan.

They remained hospitalized Friday. Bureau of Land Management spokesperson Mark Jacobsen declined to release the extent of their injuries, and attempts to learn their conditions Saturday were unsuccessful. Three of the firefighters are U.S. Fish and Wildlife Service crew members from North Dakota, and the other two are U.S. Forest Service firefighters from New Mexico.