EL CAJON, Calif. -- A big-rig hauling empty propane tanks caught fire on an East County freeway late Tuesday, causing no injuries but prompting evacuations of several nearby homes and tangling rush-hour traffic in the area.

The tractor-trailer began burning for unknown reasons on eastbound Interstate 8 in El Cajon shortly before 4 p.m., according to the California Highway Patrol.

The driver pulled over on a connector to State Route 67 and got out of the rig unharmed as the front of the truck became engulfed in flames, sending a column of thick black smoke into the air.

Police cleared residents out of houses near the interchange as a precaution. No structural damage was reported.

The accident forced the closure of the freeway connector, along with entrances to SR-67 from westbound I-8 and Magnolia Avenue. The CHP issued a traffic alert for the area.

The tanks on the rig's flatbed trailer were new and had never been filled with propane, officials said.