An accident involving a tractor-trailer rig caused a tour bus to overturn near the California-Arizona border early Wednesday morning, killing four and inuring at least 21 othersaccording to reports.

The accident occurred on Interstate 10, near Blythe, Calif., about 2:00 a.m Pacific time. The big rig apparently jackknifed onto the median and spilled its load of steel pipes onto the lanes, Terri Kasinga, a spokesman for the California Department of Transportation, told the Los Angeles Times.

The bus may have swerved to avoid the pipes or possible hit them and overturned on the shoulder. A Chevrolet Suburban collided with the pipes and was heavily damaged, according to the Times.

The bus, which carried 25 people, was traveling to Los Angeles from El Paso, Tex., with a stop in Phoenix, according to CBS Los Angeles.

There were “multiple critical and serious injuries,” Kasinga told KNX 1070, a news radio station in Los Angeles.

The road is expected to be closed in both directions at least until noon Pacific time, according to the Times.

“The later it gets into the morning, it’s going to back up in both states,” Kasinga said.

This post will be updated as we get more information…