The Elmo Fire in northwestern Montana has burned tens of thousands of acres since igniting late last month and was 55% contained as of Monday morning, officials said.

The wildfire started on July 29 in grass on the Flathead Indian Reservation. The blaze exploded in size after advancing into a forest, with tinder-dry conditions and strong winds helping the flames spread.

A total of 616 fire personnel were battling to contain the wildfire, which has scorched 21,327 acres, fire officials said.

Kelli Roemer, public information officer on the Elmo Fire on Flathead Agency, told Fox News Digital that eight total structures have been lost, including four primary residences.

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Since first igniting, the fire has forced the evacuation of about 150 residences west of Flathead Lake, KPAX-TV reported.

Aircraft dumping water on Elmo Fire

An aircraft dumps water on the edge of the Elmo Fire burning on the western shore of Flathead Lake, Montana on August 1. The wildfire was 55% contained as of Monday morning, officials said. (Hunter D'Antuono/Flathead Beacon via AP)

Evacuation orders were lifted Sunday morning for residents living along Lake Mary Ronan Road, but officials said that a pre-evacuation warning would remain in place.

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The cause of the fire is still under investigation.