(CNN) A vehicle packed with undocumented immigrants flipped Sunday, ejecting 12 people and killing at least five after a chase in south Texas, Dimmit County Sheriff Marion Boyd said.

Four people were killed at the scene about 50 miles from the Mexico border and a fifth person died at a hospital in San Antonio, the sheriff said.

Dimmit County Sheriff Marion Boyd

The incident started after a Border Patrol agent in Carrizo Springs suspected smuggling when he saw a trio of vehicles pass him on a rural highway around 11 a.m., US Customs and Border Protection said. The agent stopped one vehicle and radioed a description of the other vehicles to other agents, the agency said.

A second agent stopped the second vehicle and several people were arrested from those two vehicles, but the third vehicle didn't stop when an agent tried to pull it over, Customs and Border Protection said.

A Dimmitt County Sheriff's deputy took over the chase just west of Big Wells, but the vehicle, which was traveling around 100 mph, lost control, ran off the roadway before flipping several times, landing on the highway, according to Boyd.

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