CHAPEL HILL — A Chapel Hill Transit bus caught fire Tuesday morning, closing down a busy downtown intersection for about a half an hour.

The bus came to a rest, charred and smoking, at Franklin and North Columbia streets, just outside Spanky's across the intersection from Top of the Hill restaurant in Chapel Hill.

The Chapel Hill Fire Department responded to the fire at 10:36 a.m. and reported visible flames from the back of the bus.

"The top of it was all in flames, then it started smoking out the windows," said James Bowman, 17, an onlooker.

There were six people on the bus, including the driver, at the time of the fire, said Brian Litchfield, Chapel Hill Transit assistant director. All riders got out safely; there were no injuries.

The fire was caused by a mechanical failure and was extinguished within 15 minutes, Chapel Hill fire officials said. Firefighters continued to hack at the charred back engine, and smoke poured out of Bus No. 7480's windows after the blaze died down.

Transit, fire and police officials are still investigating the fire. Litchfield could not comment on what specifically caused the mechanical failure or how long an investigation might take.

The bus was servicing the NU route Tuesday, which runs up Martin Luther King Jr. Boulevard, through downtown and to UNC Hospitals in Chapel Hill.

katelyn.ferral@newsobserver.com or 919-932-8746