Holtville, California – A collision between a semi-truck and an SUV near the US-Mexico border on Tuesday left 15 dead and several others injured, officials said.

Twenty-five people were crammed in the SUV that struck a tractor trailer hauling gravel, said Judy Cruz, director of the El Centro Regional Medical Center emergency department.

Fourteen people died at the scene. One more died at El Centro Regional Medical Center, where six others are being treated. At least five have been flown from the scene to other treatment centers, she said.

"The patients are, of course, going through a little bit of a difficult time," said Adolphe Edward, chief executive of El Centro Regional Medical Center. "This was a major accident, and we are taking care of them in the emergency room department."

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Four people were airlifted by helicopter to the Desert Regional Medical Center in Palm Springs, where three of them are in intensive care, hospital public information officer Todd Burke said.

Deputy Fire Chief Sal Flores said the Imperial County Fire Department and the county’s Office of Emergency Services responded to a "mass fatality incident" at 6:16 AM.

El Centro Fire Department units are also on the scene, along with Customs and Border Patrol officers, who are assisting the Imperial County Sheriff’s Office.

Fifteen first responders and five fire engines arrived at the scene off Highway 115, just north of Holtville, Flores said. A helicopter whirred overhead as he responded to questions about the crash.

The cause of the collision has not been disclosed, as investigations are still underway.