The fire was reported at 4:49 a.m. just east of central Lafayette.
CHP Officer John Fransen said the driver of the carrier, which was transporting nine Chrysler sedans, heard a strange noise and pulled over on the road's right shoulder.
"He heard a loud pop, a loud noise coming from the back of his trailer," Fransen said.
When he got out of the cab to investigate, he saw that one of the cars was engulfed in flames, and that the fire was spreading.
"Seven of the nine vehicles were completely gutted," Fransen said.
Fire crews responded and put out the blaze, and no injuries were reported.
Four lanes were initially blocked, but CHP Officer James Evans said at about 8:25 a.m. that all lanes were back open except the right lane.
The charred car carrier was still on the shoulder, and a heavy-duty tow truck was on the way.
Traffic was still slow in the area.