(CNN) — Three people died and 18 were transported to nearby hospitals after a bus traveling south on Interstate 15 rolled over near Fallbrook, the North San Diego County Fire Department said Saturday.

Several people were trapped and had to be extricated from the bus when first responders arrived, the NCFD said.

It was not immediately clear what caused the crash, what company owned the bus or the bus’s destination or point of origin.

The wreck occurred around 10:30 a.m. PT (1:30 p.m. ET) on I-15 south of the Highway 76 exit, the NCFD said. Several nearby emergency agencies responded.

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