Three charter buses collided early Thursday after the brakes on one apparently failed, injuring at least 15 middle schools students on a field trip to the Atlantic coast, officials said.

The students were in a caravan of six buses headed for Myrtle Beach, S.C., when three of the buses crashed around 7:20 a.m. in Erwin, between Raleigh and Fayetteville, said Erwin police Chief Tom Chandler.

Two of the buses had stopped at a traffic light at U.S. 421 when the last bus slammed into them, Chandler said. The driver of the rear bus, Rupert Sutrall, said his brakes malfunctioned.

"It wouldn't stop," he said. "I was way on back and they must have stopped for the light. I had the brakes on and it just wouldn't stop."

There were 143 students on the three buses. Most of those taken to Betsy Johnson Regional Hospital had cuts and bruises, said Gary Pope, director of Harnett County Emergency Services.

"With three buses colliding like that, it could have been bad," he told The Daily Record of Dunn, noting that a steep embankment is next to the intersection. "Where they hit at that ravine, it could have been a lot worse."

All of the buses were from Cardinal Coach of Warsaw. A woman who answered the phone at the company's office refused to comment.

More than 30 students who had been aboard the damaged buses were to be taken back to Fuquay-Varina Middle School along with their injured classmates, while the remaining students continued to Myrtle Beach in the five buses that were still drivable, Chandler said.

Erwin police and the State Highway Patrol were investigating, Chandler said.