Witnesses said the two buses were travelling near the intersection of Hawkesbury and Ellison Roads about 3.30pm when the collision occurred.

The children suffered various injuries however all were reported to be minor, according to a police statement.

Some children were put into neck braces and taken by stretchers to waiting ambulances, while others remained on the side of the road huddled in white blankets and being comforted by friends.

“Approximately 40 children travelling on those buses are all believed to be students of St Columba's High School at Springwood,” police stated.

“The children are being transported by ambulance to both Nepean and Westmead Children’s Hospitals for assessment and treatment.”

A statement on the school's website said the buses involved were bus number 346 on the Mount Riverview to Warimoo route, and bus number 203 on the Penrith, Emu Plains and Lapstone route.

Springwood resident Tony Strahan was driving through the area on the opposite side of the road when the collision occurred.

“I heard a very loud bang and something hit me on the arm because my window was open,” he told the Gazette.

“I turned and saw one bus seemed to have smashed into the other.

“The sound was just amazing.

“It was school time so it was a 40 zone, we were not travelling fast.”

The collision caused mayhem on Hawkesbury Road, with traffic headaches for some time as emergency services worked to treat the injured and clear the scene.

Motorists travelling from Springwood to Winmalee reported sitting in the traffic for up to 45 minutes in the immediate aftermath of the collision.

Those attempting to avoid the chaos were caught in side roads as the jam snarled back through Winmalee and out onto roads leading off the Great Western Highway at Springwood and Valley Heights.

Winmalee residents Blake Dyer and Chris Gedzyk elected to abandon their car after being caught up in traffic from an earlier incident in Springwood.

“We were stuck in that and now another one, so we left the car near the hospital at the golf course,” Blake said.

Diversions were in place and police were advising motorists to avoid the area where possible to allow the flow of emergency vehicles.

All parents and families of children who were concerned were urged to contact Blue Mountains police. Tow trucks began arriving about 5.40pm and police remained at the scene for some time to determine the cause of the collision.