The crash happened on the US 281 in Encino, Texas, about 180 miles south of San Antonio.
Sergeant Nathan Brandley of the Texas Department of Public Safety said the van, designed to hold 15 passengers, was speeding as the driver tried to veer off the road onto Business Route 281.
A further 20 passengers were injured in the crash at around 4pm on Wednesday.
Texas Department of Public Safety officers (The Monitor/AP)
The driver lost control of the top-heavy van, which crashed into a metal utility pole and a stop sign.
The van was not being pursued, authorities said.
Brooks County Sheriff Urbino Martinez said he believed all of the passengers were migrants.
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