At least three people have died after a bus rolled off the highway near Fallbrook, Calif., officials confirmed on Saturday.

The North County Fire Protection District tweeted that 18 people were transported to hospitals and at least three died on the scene. They said they treated 21 patients in total. All of the surviving passengers had been removed from the bus.

The bus appeared to have rolled southbound off Interstate 15, to the south of Route 76. ABC 10 reports it was a chartered bus, and it’s not yet clear where it was coming from or where it was headed.

Village News reports that emergency officials responded to the incident at 10:24 a.m. and found multiple people who were injured, including some who had been thrown out of the vehicle. North County Fire tweeted that responders found multiple people “trapped or injured” at the scene.

ABC 10 reports that one person was found dead inside the vehicle. It also reports crews were needed to stabilize the bus to stop it from rolling further.

Officials have not released any possible causes for the crash, nor have they released a name of victims. ABC 10 reports that most of the passengers were adults but there were some minors on the bus as well.

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Write to Madeleine Carlisle at madeleine.carlisle@time.com.