Two northbound lanes of Interstate 5 north of Castaic were closed briefly Thursday due to a brush fire, creating a snarl of truck traffic that backed up for miles.

The fire broke out around 2:30 p.m. near the 36000 block of Paradise Ranch Road.

The fire was reported about a half-mile north of the freeway in an acre of medium brush running up hill with winds out of the north at 5 mph, Los Angeles County fire Inspector Quvondo Johnson said.

The Fire Department dispatched more than 100 fire trucks, along with a Super Scooper water-dropping aircraft, helicopters and a Sikorsky S-64 Skycrane to battle the blaze.

A California Highway Patrol spokeswoman said the CHP shut down the Nos. 3 and 4 lanes for about 45 minutes starting around 3:30 p.m., although the fire was in mop-up stage by then, according to Johnson. Lanes were reopened by 4:30 p.m.

The fire blackened about two acres, and no structures were damaged. The cause was under investigation.