ENCINITAS, Calif. -- A pileup Monday involving about a dozen vehicles on northbound Interstate 5 near San Elijo Lagoon left several people injured, one seriously, and snarled midmorning commuter traffic for miles, authorities said.

The chain-reaction crashes happened near Manchester Avenue in Encinitas shortly before 8:30 a.m., according to the California Highway Patrol.

Traffic slowed to a crawl in both directions and remained slow two hours after the accident, by which time all of the disabled autos had been cleared from the roadway, the CHP reported.