"If you were around the Kingston area this morning, or have any information that may assist police, please contact Queenstown Police Station on 03 441 1600."
The Otago Daily Times was been told the driver of the car was passing a truck when the collision happened.
The collision reportedly happened next to the truck's driver door.
A St John spokesman said one patient had suffered critical injuries, three moderate injuries and six minor injuries.
The patient with critical injuries, believed to be the driver of the car, was being transported to Dunedin Hospital by helicopter.
A helicopter was on the scene as of about 8am and left just after 9am.
The patients with moderate and minor injuries were being taken Queenstown Lakes District Hospital.
Otago Lakes-Central area commander Inspector Olaf Jensen said the car was heading north when it collided with the bus heading south.
Police were yet to identify the passengers and it was "too early" to determine the cause, Inspector Jansen said.
Asked about the stretch of road, where one person was killed two weeks ago when a bus collided with a car, he stressed the importance of "driving to the conditions" on what was a busy tourist highway.
St John sent two helicopters, four ambulances and one car to the scene.
The bus ended up off the road, beside the south-bound lane, near the brow of a small hill. It is upright, but on a lean.
There were multiple emergency services at the scene in the aftermath of the crash, including at least six police cars, two fire engines and ambulances.
A helicopter was sitting on road at the scene before it took off after 9am.
The Serious Crash Unit is investigating.
The crash was believed to be about 5km south of Kingston where traffic was backed up.
NZ Transport Agency said SH6 at the intersection with Allandale Rd was reopened to one lane after 10.30am.
Stop/go traffic management was in place and motorists were warned to expect "significant delays".
People sitting in the queue of traffic, which is at least 1km long on the north side of the crash, were earlier told the road may be closed for four to five hours.
The accident follows another crash involving a car and a bus carrying 14 tourists near the Devil's Staircase south of Queenstown two weeks ago in which one person died.
