MENLO PARK — Authorities say three horses were killed after they ran from a Northern California ranch onto freeway lanes, where they were struck in accidents that sent two drivers to the hospital with minor injuries.

California Highway Patrol Officer Art Montiel said the collisions on Interstate 280 near Menlo Park forced the closure of northbound lanes for two hours early Saturday.

He said the first collision was reported shortly before 5 a.m. Moments later, officers received a report that another vehicle flipped over after hitting a horse.

CHP officers found three dead horses on the freeway. A fourth horse was found unharmed farther down the interstate.

Tom Hubbard, who runs Webb Ranch just off the freeway in Portola Valley, said nobody knows how the horses escaped.