Northern California wildfire shuts down major interstate as flames devour 15,000 acres

A wildfire in Northern California that ballooned in size overnight has forced the closure of dozens of miles of a major highway and disrupted Amtrak service into neighboring Oregon.

Since igniting Wednesday afternoon in a rural area north of Lakehead in Shasta County, the Delta Fire has rapidly burned more than 15,000 acres of land, including terrain on either side of Interstate 5 near the Oregon border.

Authorities closed several miles of I-5, the West Coast's primary interstate, in both directions. Motorists were advised to use an alternate route and avoid the area, according to the United States Forest Service.

By Thursday afternoon, I-5 northbound lanes were still closed at the Fawndale exit, approximately 10 miles north of Redding, and southbound lanes remained closed 3.6 miles south of Mount Shasta at Mott Road. It's unclear when the lanes will reopen.

Union Pacific Railroad was also forced to shut down the track between Lakehead and Dunsmuir stations in California due to the fast-moving fire. As a result, Amtrak temporarily suspended its Coast Starlight passenger train service between Sacramento, California, and Klamath Falls, Oregon.

"Service will resume as soon as conditions safely permit," an Amtrak spokesperson told ABC News in an email Thursday.

The blaze spread "aggressively" overnight, with flames as high as 300 feet, the forest service said in a statement. The wildfire, which authorities described as "human-caused," expanded northwest into neighboring Trinity County. Officials would not elaborate on the exact cause of the fire.

Firefighters who are working to contain the raging flames are struggling against the region's gusty winds, hot temperatures and bone-dry vegetation, which could spur fire growth.

Meanwhile, crews are battling another blaze just east of the Delta Fire. The Hirz Fire in Shasta-Trinity National Forest has burned an area of more than 46,000 acres, but was 75 percent contained as of Thursday morning.

"Many of the eastern Hirz Fire contingency lines may be used in the efforts to control the Delta Fire," the forest service said in a statement. "Firefighters are working quickly to protect communities and structures immediately threatened by the fire."