Emergency crews responded to the scene at TransMontaigne, a Denver-based petroleum transport company with operations at the port, said Port of Brownsville spokesman Manuel Ortiz.
He said the gas leaked from a tank that holds 90,000 gallons of propane.
The leak prompted officials to shut down several nearby highways as firefighters, sheriff's deputies, state troopers and the Texas Commission on Environmental Quality worked to stop the flow of the flammable gas into the air.
No cause for the leak has been determined, Ortiz said. Both Ortiz and Perez said they did not know how many people were evacuated.
One TransMontaigne worker suffered "minor injuries" and received medical treatment, Ortiz said.
More than 230 companies operate at the Port of Brownsville, which connects to the Gulf of Mexico via a 17-mile navigation channel just north of the Texas-Mexico border.