A van with 29 migrants crashed just after 4pm on Wednesday on Highway 281 in Encino, a small village about 50 miles north of McAlly, reports the Associated Press.
Thirty people were in a van for 15 people.
The driver is among the dead, about 20 more passengers were injured, all of them in serious or critical condition.
Brooks County Sheriff Urbino Martinez said the van was designed for only 15 passengers and that it was too heavy when the driver lost control and overturned.
Sheriff Martinez said police were not pursuing the van.
No information about the van, such as who it belongs to, is disclosed.