DANVILLE -- A crash involving two cars and a big rig leaking gas briefly blocked three lanes of northbound Interstate 680, officials said.

The collision was reported around 7:20 a.m. just north of Diablo Road. Two ambulances were sent to the scene, though the extent of injuries is unknown.

The big rig is on the side of the road and is leaking gas from one of the tanks on the cab, according to a California Highway Patrol dispatcher. The truck is not a tanker.

The left two lanes were briefly blocked, but have been cleared. The right lane was still cleared around 8 a.m.

A SigAlert was issued as traffic backed up past Greenbrook Drive, but was lifted around 9:15 a.m. Traffic appears back to normal, according to Sigalert.com.

Contact Daniel M. Jimenez at 510-262-2728. Follow him at Twitter.com/DMJreports.