Emergency services are at the scene of a crash involving an Otamatea High School bus in Northland.
St John says the crash near the intersection of State Highway 1 and the State Highway 12 Dargaville turnoff happened about 8.20am.
Three ambulances were sent to the scene, where at least seven patients were treated.
The crash involved two other vehicles - a car and a truck.
Police said at least two people have been moderately or even seriously injured - they were being treated by St John paramedics.
Five of the patients have been taken by ambulance to Whangārei Hospital.
Another 18 students made their own way to the school, and 10 were treated for minor injuries.
Otamatea High School said it was supporting the students involved in the crash.
"The school remains open for instruction as normal and we will continue to offer support to all the students and their families at this time."
Kaipara District Mayor Jason Smith said the bus had picked up students from the Kaiwaka and Mangawhai districts.
"We're just extremely concerned for these patients and the students of OHS [Otamatea High School] and the drivers of the other vehicles as well, that everyone is well and safe and gets home at the end of the day. That's the most important thing," he said.
"We don't have a fatality and that is a blessing in this situation."
He said the community was aware of how vulnerable school buses were on open roads, and since the Highway Cafe closed at the junction it had been an empty stretch of motorway.
"The Brynderwyn intersection is a very challenging piece of road because traffic is coming off SH1 often at high speed onto SH12 so you have a confluence of roads and a carpark and pulling over bay."
Electronic signs alert motorists on State Highway 1 to slow from 100km/h to 60km/h when a sensor detects a vehicle approaching the intersection.