LIVERMORE -- Two drivers sustained serious injuries in a three-vehicle collision early Monday morning on Vallecitos Road just north of the main entrance to Ruby Hills.

The accident occurred shortly before 6:30am when the truck sideswiped the left rear side of a Honda Civic, causing the driver of the Honda to lose control and slide sideways into oncoming traffic. The Civic slid into southbound traffic, where a Jeep struck the vehicle, seriously injuring both drivers.

The incident tied up rush-hour traffic as far back as Isabel Avenue.

"This was the worst possible time for an accident on Highway 84," said Sgt. John Hurd, a spokesman with the Livermore Police Department.

The driver of the pickup did not stop and continued northbound on Isabel Avenue.

The department is continuing to investigate the cause of the crash and search for the driver of the pickup. "We would like to speak with anyone who witnessed the accident," Hurd said.

Livermore Police encourage anyone who may have witnessed the accident to call Officer Traci Rebiejo at 925-580-9665.

Contact Karina Ioffee at 650-576-9626. Follow her on Twitter at Twitter.com/kioffee