PORT BARRE, La. — A tractor-trailer slammed into a school bus that had its lights flashing and stop signs extended, critically injuring three children and hurting the other 18 and both drivers, Louisiana State Police said today.

The bus driver — who also is a town mayor — and the trucker both had minor injuries, said Trooper Stephen Hammons. Most of the children, ranging in age from 5 to 17, had minor to moderate injuries, while two of those critically injured were ages 5 and 15, Hammons said.

The crash happened around 7:30 a.m. on a straight, clear stretch of U.S. 190 between Port Barre and Opelousas, about 50 miles west of Baton Rouge.

“The back bumper was pushed in almost all the way to the rear wheels of the bus,” said Eric Thibodeaux, supervisor on site for Acadian Ambulance Service.

The bus was driven by Port Barre Mayor Gil Savoy, 67, a retired school bus driver who was working as a substitute. The truck driver, 52-year-old David Cox of Dallas, was not immediately cited, but the investigation is ongoing, Hammons said.

He said the bus was just starting to leave the bus stop with its warning lights flashing and its stop signs extended.

Savoy’s wife, Camilla Savoy, told a reporter that he told her he looked in his rearview mirror, saw the big rig bearing down on his bus and yelled to the children to brace themselves. He grabbed the steering wheel and managed to keep the bus on the road, Camilla Savoy said.