Strong winds have blown over a school bus on the Waikato side of the Kaimai Range causing minor injuries to the driver and one of the two school children on board.

The cause is a weather phenomenon known locally as the ‘Kaimai Buster' that amplifies easterly winds into a gale force punch, which occurred on the Old Te Aroha Road.

Matamata Piako District Council has closed the Te Aroha-Gordon Rd and Old Te Aroha Rd to heavy traffic and motorcycles until further notice due, because of the severe weather conditions.

Other vehicles should avoid the route if possible, and take extreme care, says the council.

An aerodynamic effect of the Kaimai Ranges turns strong easterlies into winds a person can struggle to remain upright in, says Matamata Police Sergeant Graham McGurk.

The 52-seater bus was shunted over and off the road while driving to school along Old Te Aroha Road.

The winds nearly blew over the ambulance called to treat the injured, say police.

'The ambulance nearly got blown over, just standing there,” says Graham.

'The wheels started coming off the ground so we had to move it."

The winds have in the past blown over trees, barns and pushed vehicles off the road. Graham understands another car was blown off the road near Te Aroha.

'These Kaimai Busters stop as quickly as they start,” says Graham.

'You have got to get the right aerodynamic effect. We have a mild form quite often. It seems to happen with an extreme low, like what's coming down now.”

"A huge low pressure runs under the range during strong easterly winds and it just rushes down. You get about a kilometre-wide area that receives very strong winds, but in Matamata there wasn't a breath of wind.”

It is a freak weather event and it is hard to predict when or where it will strike.

The accident is being investigated by the Commercial Vehicle Inspection Unit. It's not known when the road will reopen.