Five members of a Southern California family were killed Saturday when their van was rear-ended by an 18-year-old driver who was later arrested on suspicion of driving under the influence, authorities said.

The dead were among seven family members who were in the van, authorities said. The other two -- the 40-year-old female driver and a 15-year-old boy -- were hospitalized in critical condition.

Jean Soriano of California was booked into the Clark County Detention Center after he was treated and released at University Medical Center in Las Vegas, Nevada Highway Patrol Trooper Loy Hixson said.

The crash happened at about 3 a.m. on Interstate 15 near the Utah line. Soriano's sport utility vehicle struck the van from behind, causing both vehicles to spin out of control and roll near Mesquite, some 80 miles northeast of Las Vegas, investigators said.

A 23-year-old passenger in Soriano's SUV was treated at the hospital and released.

Authorities believe Soriano was returning from a visit with family in Utah to his home in California at the time of the wreck, Hixson said. They didn't immediately release his hometown or the names or hometowns of the victims.

Beer bottles were found in the SUV, Hixson said, and troopers performed a blood-alcohol test on Soriano at the hospital. The results won't be known for a couple of weeks, he said.

Hixson said only two of the seven people in the van were wearing seatbelts. The five who were not buckled in were ejected, but one survived.

"Unfortunately, so many in the van weren't wearing seatbelts, and some might have survived had they been wearing them," Hixson said. "We see it so many times where people can survive simply by having a seatbelt on."

The van was carrying a couple, their children and some aunts and uncles, he said. Killed were three men in their 40s, a teenage female and an adult female.