US authorities on Monday charged the driver of the overheated truck found in Texas packed with migrants, 10 of whom died, with one count of transporting illegal immigrants, prosecutors said.

The US Attorney's office charged James Matthew Bradley Jr, 60 with one count of "transporting illegal aliens" -- punishable by life imprisonment or the death penalty -- after authorities found 39 migrants had been crammed in the trailer parked in the baking Texas heat.

In announcing the charges, immigration authorities said they believed more than 100 people were in the truck at one time, with many thought to have escaped.