He said one patient was deceased at the scene and another patient had serious leg injuries and was taken by ambulance to Christchurch Hospital.
Three other patients were treated at the scene, but not transported.
Woodend Volunteer Fire Brigade Chief Fire Officer Murray Lamb said it was a "very, very sad" accident.
"It looks like the motorcycle may have hit the back of the car and that knocked them off in front of the oncoming traffic," he said.
Early indications suggested the motorcycle was travelling south and hit the back of a car as it turned right into Harleston Rd, knocking off the driver and passenger into the path of an oncoming car and van.
"Unfortunately the female passenger of the motorcycle has gone up under the front of the van and was trapped."
Canterbury Westpac Rescue Helicopter crewman and paramedic Wayne Legerwood said the service airlifted a paramedic to the scene, and then carried on to another serious car accident nearby.
"We got diverted to that from another job that we were heading to. We landed and there was one patient there with some rather nasty and serious leg injuries," he said.
The intensive care paramedic stayed at the scene, while the helicopter carried on to another car accident in the Ashley Gorge where a man was trapped in his car for two hours after it left the road about midday.
Southern police communications shift inspector Peter Hegarty said police were working to identify the deceased patient.
SH1 was closed near the accident, he said.
Police's Serious Crash Unit was at the scene.
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