UPDATE 5:00 p.m.: California Highway Patrol is currently lifting the closure from the slow lane on southbound Highway 101, according to a CHP dispatcher.
Drivers are experiencing medium traffic along Highway 227 caused by drivers attempting to avoid southbound Highway 101, the dispatcher said.
Cal Fire received the report of fire at approximately 1:30 p.m. according to CHP's online incident report.
UPDATE 4:00 p.m.: Air tanker retardant halted the 7-acre fire's forward spread and Cal Fire declared it contained at 3:24 p.m, a dispatcher said.
Cal Fire's air crafts have been released, but ground equipment remains on the scene.
A California Highway Patrol dispatcher said the fire is on Ontario Road next to southbound Highway 101 and north of San Luis Bay Drive. CHP closed the highway's slow lane at 3:52 p.m.
Cal Fire first responded to reports of the fire at approximately 2:30 p.m.
ORIGINAL STORY: Cal Fire is responding to a 7- to 8-acre fire west of southbound Highway 101 a mile or two north of San Luis Bay Drive in San Luis Obispo.
The fire is spreading uphill and threatening homes, a Cal Fire dispatcher said. Cal Fire is on the scene with 15 engines, four air tankers, two dozers and two crews.
The cause of fire and number of threatened homes is not yet known.
More information will be posted as it becomes available.