BIG WELLS, Texas - At least five people were killed and several others hurt Sunday as an SUV carrying more than a dozen people during a suspected "smuggling event" crashed while fleeing from Border Patrol agents in South Texas, authorities said.

The SUV carrying 14 people went out of control at more than 100 mph and overturned on Texas Highway 85, ejecting most of the occupants, Dimmit County Sheriff Marion Boyd said.

"From what we can tell the vehicle ran off the road and caught gravel and then tried to recorrect," Boyd said, adding that "caused the vehicle to turn over several times."

Four victims were dead at the scene, Boyd said. He said at least one and possibly two others died at a hospital.

The Border Patrol said in a statement Sunday night that two other vehicles had been travelling alongside the SUV earlier in the day. An agent suspected they were conducting a "smuggling event," according to the statement, which did not elaborate.

The border agent stopped one of the vehicles and another agent stopped a second one. Multiple people from both vehicles were arrested.

The third vehicle kept going when agents encountered it, and a sheriff's deputy took over the chase prior to the fatal crash, the border patrol said.

The incident comes amid heightened tensions over the treatment of immigrants at the southern border. The Trump administration has said tougher immigration policies - even separating children from their parents - are needed to deter immigrants from coming to the country illegally. Over a six-week period ending in May, about 2,000 children had been separated from their families, administration officials said Friday.

Most of the occupants in the SUV were believed in the country without legal permission. Boyd said the driver and one passenger were believed to be U.S. citizens. The driver was among those hospitalized, and a deputy who assisted the Border Patrol with the chase found the driver sitting upright in his seat and took him and the passenger into custody.

"This, I think, is a perfect example, of why are borders need to be secured," Boyd said.

Some injured were taken by helicopter to San Antonio, about 144.83 kilometres northeast. Dimmit County is directly north of Webb County and east of Maverick County, which border Mexico.

"Our deepest sympathies go out to the families of those who died in the crash," The Border Patrol said in the statement.