Five patients were in serious condition following the collisions shortly after 1 p.m. that shut down all lanes on Interstate 405 in the city's San Fernando Valley area, Los Angeles Fire Department spokeswoman Margaret Stewart said. The 20 others were in fair condition with minor injuries. A total of 40 people were evaluated at the scene, she said.

The California Highway Patrol was investigating the cause of the pileup on the key north-south artery.  It wasn't immediately known how many people were on the bus or where it was headed.

Television news footage showed a white charter bus marked "Transit Systems" splayed sideways but upright across southbound lanes in the North Hills neighborhood. Its skid marks indicated it had gone sideways on the northbound side and then through the divider, City News Service reported.

The bus's front end was crumpled, and emergency window exits were popped open.  An SUV next to it had extensive front-end damage.

At least one crashed vehicle was in northbound lanes, which were reopened by about 2:30 p.m. The southbound side remained closed hours later, backing up traffic for miles. Some motorists stuck in their cars walked off the freeway, apparently in search of toilets or drinks, City News Service reported.

The patients in serious condition were three women, ages 49, 60 and 88, and two men, ages 30 and 69, Stewart said.

Nobody answered at a phone number listed for Los Angeles-based Transit Systems bus company.