A disabled big rig blocked a southbound Highway 101 lane in Petaluma early Tuesday, causing an extensive backup to the morning commute, said the CHP.

The rig was in the center lane, south of East Washington Street.

The CHP issued an alert to warn drivers of an area slowdown.

A CHP dispatch log showed the problem started at about 7:10. a.m.

A big rig tow truck was called but initially it was unclear how long it would take to clear the huge vehicle, according to the CHP.