A pickup truck pulling a horse trailer crashed in Southern California on Saturday, injuring more than a dozen people who may have been in the U.S. illegally, according to reports.

The Ford F-250 and the trailer that it was pulling got separated while driving and the haul toppled over, The San Diego Union-Tribune reported, citing the California Highway Patrol (CHP). After the trailer spilled onto the road, several people ran from the scene before they were found, officials said.

As many as 20 people were inside the trailer and up to 18 received treatment, Cal Fire Battalion Chief Kurt Zingheim said.

Six people were sent to the hospital for medical treatment, The Union-Tribune said, while others received treatment on location and reportedly were arrested.

The identity of the driver wasn’t known, Border Patrol told the outlet, and they didn’t immediately know if the individual was in custody.