HOPEWELL TOWNSHIP, NJ (CBS) – Authorities are investigating a crash in Mercer County that involved three cars and a small school bus.

The crash happened around 8:30 a.m. at the intersection of Hopewell Princeton Road (County Route 569) and Crusher Road, when a Hopewell Valley Regional School District bus was traveling north on Hopewell Princeton Road and attempted to turn left onto Crusher Road.

As the bus was turning, it was hit by a vehicle heading south on Hopewell Princeton Road operated by Heather Haynes, a 36-year-old from Blairstown, NJ. The impact caused the bus to spin and turn over on the driver’s side. It came to rest on the hood of a vehicle that was stopped at the Crusher Road intersection and was operated by 34-year-old Brigid Finn, of Hopewell.

After colliding with the bus, Haynes’ vehicle spun around and entered the northbound lane of Hopewell Princeton Road, where it was then hit by a car heading northbound operated by Magdalena Fiedosiuk, a 32-year-old from Baltimore.

Officers responding to the scene discovered the bus on its side in the intersection and partially on top of another car. Two additional cars were involved.

The only student on the bus, a four year-old male from Hopewell Township who was being transported to a preschool program at the Bear Tavern Elementary School in Titusville (Hopewell Township), was already off of it when officers arrived at the scene, and an aide who was also riding the bus was able to exit on her own shortly thereafter. All of the other occupants of the three cars were already outside and complained only of minor injuries.

The bus driver, Rebecca Medina, was trapped on the overturned bus, but firefighters were able to extract her.

All of the injured were transported to Capitol Health System’s Hopewell Campus.

The crash remains under investigation.