A bus filled with preschool children careened into a guardrail after hitting a pole along the Schuylkill Expressway Thursday morning, a passenger and officials tell NBC10.

The bus, carrying 24 children and six adults from Hope Church School in the East Oak Lane section of Philadelphia, was traveling eastbound on the highway near the Girard exit when the crash happened around 10 a.m. The preschoolers were heading to the zoo for a field trip, a school official said.

Sharneca Reid was on board the bus chaperoning the trip for her daughter's class. She said the bus hit a light pole and then rammed head first into a guard rail.

The pole could be seen sticking out from underneath the bus as the children were moved to a second bus.

State police said the driver lost control of the bus as it negotiated a slight curve.

Reid said the kids have some minor injuries and are being taken to the Children's Hospital of Philadelphia for treatment. Several adults were taken to Hahnemann University Hospital. A school official said they're being taken as a precaution.

The crashed closed two lanes for two hours and backed up traffic on the highway for miles.

This story is developing. Check back for updates.