50 children involved in Blue Mountains bus crash

Four people have been taken to hospital after two buses collided in the NSW Blue Mountains.

According to police, 68 people were on the two vehicles that collided on State Mine Gully Road in Marrangaroo near Lithgow about 3.50pm.

Officers say 50 children were involved in the crash at the intersection of Clarence Road, where one bus rear-ended another.

It's believed the children involved were on a school holiday excursion from St Marys.

"A major emergency response has been activated involving officers from Lithgow general duties and Chifley Highway Patrol, NSW Ambulance Paramedics, Fire & Rescue NSW, and volunteers from Lithgow VRA," a police spokesperson said on Thursday.

"At this time, police have been told the worst injuries appear to be related to bruising; however, three children and one woman have been already been taken to Lithgow Hospital for further assessment."

All children involved in the crash are being checked at Lithgow Hospital as a precaution.

A third bus arrived at the scene to transport the children, who were believed to be primary school aged and younger.

Anyone with information on the crash is urged to call Crime Stoppers on 1800 333 000 as the investigation continues.