SPRINGERVILLE, Ariz. — A raging forest fire in eastern Arizona that has forced thousands from their homes Wednesday is headed for a pair of transmission lines that supply electricity to hundreds of thousands of people as far east as Texas.

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

The blaze has blackened about 389,000 acres and destroyed 11 buildings, primarily in the Apache-Sitgreaves National Forest. No serious injuries have been reported.

Fire crews had furiously worked to protect the town of Eagar and Springerville on Tuesday, and it appeared to pay off. They created barriers between the towns and the fire and burned out combustible material, such as brush and trees.

“It’s looking good to us. It did what the team said it would do when it came over the hill toward town,” Apache County Sheriff’s Office Chief Deputy Brannon Eagar said. He added: “It worked out perfectly.”

The fire prompted Texas-based El Paso Electric to issue warnings of possible power interruptions for its customers in southern New Mexico and West Texas.

The company uses two high voltage lines to bring electricity from the Palo Verde Nuclear Generating Station west of Phoenix to the two states. Losing the lines would cut off about 40 percent of the utility’s supply, possibly triggering the rolling blackouts among its 372,000 customers.

About half of the 4,000 residents who call Eagar home were forced to leave Tuesday as the fire licked the ridges surrounding the area. Those in neighboring Springerville worried as they awaited word of whether they too will have to flee.

On Wednesday afternoon, authorities ordered more evacuations as the wildfire pushed closer to Eagar
and Springerville.

The blaze, burning in mainly ponderosa pine forest, was sparked May 29 by what authorities believe was an unattended campfire. It became the second-largest in Arizona history on Tuesday.

It has cast smoke as far east as Iowa and forced some planes to divert from Albuquerque, N.M., some
200 miles away.

Thousands of firefighters, including many from several western states and as far away as New York, are already helping.

With a blaze as large as this being driven by unpredictable and gusty winds, putting the fire out is a gargantuan task.

All fire managers can do is try to steer it away from homes and cabins by using natural terrain, burning out combustible material first and trying to put out spot fires sparked by embers blowing in front of the main fire front.

The cost of fighting the blaze has approached $8 million. Officials said it is likely to get more expensive.