A big rig caught on fire and ignited a patch of nearby brush on the northbound Interstate 5 a half-mile north of Templin Highway late this morning, closing all but two lanes for a while as firefighters worked to douse the blaze.

The fire started around 11 a.m. due to a fuel leak, a Los Angeles County Fire Department spokeswoman said.

The big rig disconnected from its trailer and caught on fire, one witness said. The fire spread to brush on the side of the freeway and burned a quarter-acre before firefigthers extinguished it, he said. The blaze was reported out by 11:30 a.m.

Firefighters were concerned that the big rig’s full fuel tanks would spill into nearby storm drains, the witness said. Northbound traffic was backed up for a mile because of the fire.