UPDATE: includes info on cancelled SIGalert and traffic conditions on the southbound 5 freeway. 

Traffic is still slow after a semi-truck overturned on the southbound 5 freeway Saturday morning, blocking traffic heading towards Los Angeles for several hours.

Witnesses reported at 11:40 a.m. another collision involving a big-rig, as well as several military vehicles that had pulled off of the 5 due to the traffic shutdown were causing further delays in the southbound lanes north of McBean Parkway.

The crash was reported at 9:17 a.m. near Weldon Canyon, and California Highway Patrol officers were on scene with ten minutes.

According to official CHP records, the big-rig overturned, blocking the # 1, 2, 3 and 4 lanes. Several cars hit the overturned vehicle after the initial crash.

A SIGalert was issued until approximately 11:30 a.m. by officials, so they could work to clean up the crash site and tow any vehicles involved in the collisions out of the way. All lanes were declared open and the SIGalert was cancelled shortly after 11:30 a.m.

Nobody at the scene had serious injuries, fire officials said.

“The squad did not follow up on a transport,” said Supervising Fire Dispatcher Cheryl Sims. “We went available at 9:51 (a.m.).”

Traffic heading southbound along the 5 is severely impacted by the incident, with almost all of the traffic through Santa Clarita crawling at less that 10 MPH.

Witnesses are reporting surface streets such as the Old Road have become backed up as well due to motorists attempting to avoid the freeway.