SPRINGERVILLE, Ariz. — Fire crews worked through the night to protect several Arizona mountain communities from a growing forest fire that has forced thousands from their homes and threatens transmission lines that supply electricity as far east as Texas.

The 607-square-mile blaze, the second largest ever in Arizona, is expected to reach the power lines as early as Friday. If the lines are damaged, hundreds of thousands in parts of New Mexico and Texas could face rolling blackouts.

Meanwhile, crews are hopeful they can slow the fire today if weather predictions hold. After a few days of driving winds, there was no high-wind warning issued for today.

Residents remaining in Springerville and the neighboring community of Eagar were evacuated Wednesday as a spot fire popped up on the northwestern edge of the Wallow Fire. That caused officials to worry about the prospect of the fire hooking around a bulldozer line and a burned out area and racing toward town.