Firefighters briefly closed Interstate 580 near Corral Hollow Road on Friday evening because thick clouds of smoke from a 2,000-acre wildfire had obscured the road.

By 6 p.m., the road was open again, though the air remained smoky.

The fire started Friday afternoon near Site 300 at the Lawrence Livermore National Laboratory and sent clouds of brown-gray smoke across the skies south of Tracy.

It’s unknown how the fire started, though it was first reported about 4:30 p.m., according to lab spokesman Steve Wampler. He also said that no injuries were reported and no buildings were burned.

Crews from the Tracy Fire Department that raced up Corral Hollow Road at first were called off by firefighters near Site 300, the lab’s explosive test site just a few miles west of Tracy.

But firefighters reported that the fire quickly jumped a lab fire line.

Once it left lab property, it spread from about 25 acres to more than 100 acres within minutes as it roared through Corral Hollow Canyon, firefighters said.

As of 7:30 p.m. Friday, the fire was 75 percent contained.

But firefighters reported that fire quickly jumped a Lab fire line.

Once it left Lab property, it spread from about 25 acres to more than 100 acres within minutes as it roared through Corral Hollow canyon, firefighters said.