Four people were killed and two were critically injured in an auto wreck when a car veered off a mountain road near Wrightwood, California, early on Friday.

“For unknown reasons, the vehicle swerved away from the roadway, struck a telephone pole and rolled down an embankment. At that time, four parties were ejected from the vehicle,” California Highway Patrol Officer Thaniel Ong told ABC 7.

The crash, which was called in around 1:30am, occurred on Highway 2, between Big Pines and Wrightwood, near the LA-San Bernardino County line.

Most of those inside the 2016 Hyundai Veloster were not wearing seat belts and alcohol is thought to be a contributing factor to the crash, according to officials.

According to CHP, all six people involved in the crash are from Wrightwood, a town of about 5,000 people in the mountains north of Los Angeles.

The dead include two women and two men.

Responding to the scene involved a complicated rescue process because most of the occupants were scattered outside the car and responders didn’t know how many people had been inside, Chris Prater, a public information officer for the San Bernardino County Fire Department, told The Los Angeles Times.

Upon searching the scene, responders found five people had been ejected from the car, and a sixth person, who had been wearing a seat belt, took it off and exited the vehicle.

Four people were confirmed dead on the scene, while two were flown by air ambulances to Arrowhead Regional Medical Center in Colton in critical condition.

“The CHP reminds all motorists and passengers that seat belts save lives,” the agency told the paper. “Wearing a seat belt is the single most effective action a person can take to protect themselves in the event of a traffic collision.”

“Impaired driving is illegal, dangerous, and entirely preventable,” the statement added. “If you plan to consume alcohol, designate a sober driver, use a rideshare service, or contact a friend or family member.”