Forty Brazilian immigrants were found loaded inside a stifling tractor-trailer about 75 miles north of the Mexican border, authorities said. No injuries were reported.
Border Patrol agents discovered the immigrants Saturday at a highway checkpoint in Falfurrias, officials said. A patrol dog alerted agents to the scent of people.
"As soon as those agents opened the back of the trailer, they could just feel the heat coming from inside," said Border Patrol spokesman Oscar Saldana.
The driver, a U.S. citizen, was charged with smuggling, but his identity was being withheld.
The immigrants - including men, women and children - are being processed for deportation, officials said.