At least 13 people were killed in southern California on Tuesday when a vehicle packed with passengers collided with a large truck in a "chaotic scene" close to the Mexico border, officials said.

The accident occurred when the SUV carrying more than two dozen people -- including minors -- and a semi-truck full of gravel crashed near El Centro, California, Judy Cruz, an official from El Centro Regional Medical Center said.

The area of the state is a thoroughfare for Mexican immigrants and farmworkers headed north towards California's rich agricultural center, but officials said it was still unknown whether the passengers were migrants.

"It's too early in the investigation to say what they were doing and where they were coming from," Omar Watson of the California Highway Patrol said during a Tuesday afternoon press briefing.

A total of 25 occupants, including a driver, were traveling in the SUV at the time of the crash, he told reporters earlier in the day.

"We had 12 fatalities on scene, one person passed over at the hospital, a total of 13 people passed away," he said. Among the dead was the SUV's 22-year-old driver.

However the El Centro Regional Medical Center reported that 15 people had died and that the SUV contained 28 individuals.

The Ford Expedition SUV would have a legal capacity of about eight people, according to the carmaker's website.

Images of the collision showed the semi-truck crashed into the side of a burgundy-colored SUV that appeared to have California license plates.

According to Watson, the accident occurred when the SUV entered an intersection in front of the semi-truck, although it was not known whether the smaller vehicle had stopped at the stop sign.

Children injured

"Some people were ejected onto the pavement, onto the ground, that passed away as a result of those injuries," Watson said. "Other people were found deceased within the vehicle."

At the afternoon press conference Watson described the crash site as "a pretty chaotic scene."

The cab of the truck was almost intact but the SUV, although still on its four wheels, was badly damaged.

Watson also said that "there were children in the vehicle but we don't have all the ages yet," later specifying that they were "not young children."

Those killed ranged in age from 20 to 55, but at least one of the injured was a minor age 16.

The wounded, including the 69-year-old driver of the semi-truck who sustained moderate injuries, were transported to various regional hospitals where they were being treated for "minor to very severe" issues, Watson said.

"We are working with the Mexican consulate to determine exactly who was in the vehicle and make sure we notify the next of kin," Watson said, without specifying the nationality of those involved in the accident.

"A lot of people in the vehicle didn't speak English," he said, adding that "we are close to the border so we have people that come back and forth on a daily basis for work."

The collision occurred shortly after 6:00 am on State Route 115 near the town of Holtville, about 10 miles (16 kilometers) north of Mexico.

The accident was not a Border Patrol pursuit, Watson said, adding that "we're not exactly sure what caused the collision but there were no law enforcement involved."

Crashes involving high death tolls are not uncommon along the California-Mexico border during chases with US border authorities, according The San Diego Union-Tribune.

Separately, a series of harrowing collisions involving vehicles carrying farmworkers en route to the state's Central Valley agricultural region led to the passage of legislation requiring vans and buses carrying nine or more workers to have seat belts and undergo annual safety certification, the newspaper said.