A wildfire erupted along Interstate 80 near the California-Nevada state line Wednesday morning and exploded in size within hours, forcing evacuation orders, shutting down a vital mountain freeway and sending crews scrambling through the night to keep it from reaching the Reno-Tahoe corridor.

The Floriston Fire ignited around 10 a.m. near I-80 and Floriston Way, roughly nine miles northeast of Truckee, according to Cal Fire. By evening it had scorched 613 acres and was only 5 to 6 percent contained, fed by gusty winds and tinder-dry fuels under a Red Flag Warning.

Westbound I-80 was shut down at the Nevada state line and stayed closed overnight, with Dog Valley Road also blocked and officials warning drivers against dodging the closure on rural backroads. Nevada County issued a mandatory evacuation order for the zone closest to the flames, while Sierra County and Nevada's Washoe County put out evacuation warnings for a wider swath of communities from Floriston toward Verdi and Mogul, just west of Reno, according to KOLO 8 News Now.

Crews battled through the night

More than 20 fire engines, a dozen hand crews, 10 water tenders, eight bulldozers and multiple aircraft — including night-flying helicopters — were thrown at the blaze as it pushed east through the afternoon, per Cal Fire's incident report. CBS Sacramento reported the fire was moving at a "dangerous rate of spread" and threatening the Truckee River watershed, a critical water source for the region, as well as infrastructure along the interstate.

"Fires can change quickly."

That was the warning Washoe County emergency officials gave residents even as they briefly downgraded some evacuation orders to warnings Wednesday afternoon, only to watch the fire keep growing into the evening, according to local reporting from the scene.

No injuries have been reported, and as of Wednesday night the fire had not crossed into Nevada, though it burned dangerously close to the state line in country popular with hikers, anglers and cabin owners along the Truckee River. Cal Fire had not confirmed any structures lost. The cause of the fire remains under investigation.

The blaze is the latest in a punishing stretch for the Sierra Nevada and Great Basin region, where Red Flag conditions — low humidity, dry vegetation and gusty afternoon winds — have kept fire crews on edge through mid-September. For now, officials say the priority is holding the line along I-80 and the watershed while assessing whether the closed freeway, a main artery between Sacramento and Reno, can reopen once winds ease.

Fire officials are expected to issue an updated containment figure and evacuation map Thursday morning as day-shift crews take over from the overnight helicopter operation.