The Timber Fire has burned to nearly 3,800 acres above Big Sur with containment at 5 percent, threatening named coastal landmarks and forcing a 10-mile closure of Highway 1 as lightning drove crews off containment lines Wednesday afternoon.

Over 500 structures in Big Sur were under threat Wednesday — among them Nepenthe, Alila Ventana Big Sur, The Sur House, and Sierra Mar — as the Timber Fire burned through nearly 3,800 acres of steep coastal terrain with containment at 5 percent, according to Cal Fire and NBC Bay Area.

Highway 1 has been closed for a 10-mile stretch southeast of Loma Vista since Tuesday, severing the main road through a community that depends on it. Cal Fire Battalion Chief Josh Silveira, speaking at a virtual media briefing Wednesday, did not minimize the cut. "We don't take those road closures lightly," he said.

The fire started Sunday southeast of Loma Vista and spread rapidly, pushing active flame along Partington Ridge, Coast Ridge Road, and both its northern and eastern flanks, according to SFGate. Ground crews and bulldozer operators built containment line near Partington Ridge while protecting structures east of the highway between Ventana and Partington Road.

By Wednesday afternoon, a new hazard arrived. Cal Fire announced that cloud-to-ground lightning strikes were forcing crews off the containment lines entirely. "Conditions across the Timber Fire are generating active cloud-to-ground lightning strikes, forcing ground crews to temporarily disengage from containment lines and fall back to designated safe zones for firefighter safety," the agency said. A 15 to 20 percent chance of thunderstorms through the evening brought erratic wind gusts and atmospheric instability on top of terrain that, as Silveira put it, "we can't change."

As of Wednesday, 640 residents were under evacuation orders and roughly 350 more under evacuation warnings, according to Monterey County's Department of Emergency Management. An overnight shelter was established at Carmel Middle School; three people stayed there Tuesday night. More than 900 firefighters from across California were assigned to the blaze.

The Community Foundation for Monterey County has opened a fundraiser for displaced residents at cfmco.org.