The bus, carrying 25 children on an excursion, was heading downhill near the Mt Pleasant Road overpass when the brakes failed on a truck loaded with timber travelling behind.

The truck driver tried to avoid the bus by overtaking it on the inside lane but clipped its left-hand side.

The truck careered past the bus before heading back to the middle of the roadway, striking the jersey barrier and flipping onto the other side of the road.

Incredibly, the truck avoided colliding with oncoming traffic and eventually came to rest on its wheels in the northbound lanes.

Police, fire and ambulance crews were immediately called to the scene of the accident which occurred about 10am.

Paramedics quickly ascertained no children were injured.

There were initial fears the 24-year-old truck driver may have been trapped in his vehicle. However emergency crews found he had managed to free himself from the wreckage.

He was taken to Wollongong Hospital with a head wound.

One of three northbound lanes was blocked due to the accident and police closed all three lanes for a short time while they removed the truck.

While emergency crews were on the scene, there was a call to attend a second accident 500 metres up the hill on the southbound side of the road.

Due to the bank-up of traffic from the first accident, a truck had run into the back of a car, police said.

There were no serious injuries.

The accident, and a fuel spillage on the road, forced the temporary closure of one of the two southbound lanes while fire crews cleaned up.