By Patrick T. Fallon

VENTURA, Calif. (Reuters) - A wildfire northwest of Los Angeles burned about 1,200 acres of land, forced the closure of parts of a major highway and led to evacuations on Saturday, fire officials said.

More than 600 firefighters battled the blaze in the Solimar Beach area of Ventura County, and parts of U.S. Highway 101 were closed for part of the day, county fire department officials told a news conference.

No injuries have been reported, fire officials said. No structures have been damaged by the fire, but nearby Union Pacific rail lines were closed for a period and the fire is a threat to oil, gas and power lines.

The northbound side of the highway, a major roadway in the region, reopened around 2 p.m. local time (5 p.m. ET) according to state transportation officials, and the southbound side was moving 30 minutes later according to a Reuters witness.

At 1:30 p.m. local time, an Amtrak train heading north and filled with passengers passed near Solimar Beach, according to the same Reuters witness.

"Even if we do open up the roadways, it's still not a contained fire," Ventura County Fire Department Chief Norm Plott told reporters earlier in the day. "It's a very dynamic fire. We're not quite out of the woods yet."

The fire is less than 10-percent contained and it will take at least three days to get it under control, fire officials said. The cause of the fire was still under investigation.

Helicopters and fixed-wing tankers were helping to battle the blaze with water drops.

Fire officials had earlier reported that parts of the Pacific Coast highway also were closed, but a fire department spokeswoman said only a portion that overlaps the 101 was closed. Ventura is about 65 miles (105 km) northwest of Los Angeles.

The fire started at around 11 p.m. local time on Friday near Ventura, and strong winds as high as 50 miles per hour and dry vegetation caused it to grow rapidly, fire officials said.

At around 2 a.m. local time on Saturday in a video posted on Facebook, Ventura County Fire Department Captain Steve Kaufman said the fire was near the beach, "bumping up against the roadway. We're getting a bunch of embers in Solimar east."

The Solimar Beach community, with 50 to 60 homes, and a nearby campground were under a mandatory evacuation order, while a voluntary one had been issued for the nearby Faria Beach community, where there are 30 to 40 homes, fire officials said.

(Writing and additional reporting by Ben Klayman in Detroit; Editing by Pravin Char, Hugh Lawson, Dan Grebler and Bill Rigby)