Emergency services are responding to a two-car crash on State Highway 25 near Tararu, just north of Thames.
A Fire and Emergency spokesman said one person had been extracted from a vehicle, while three people were being assessed by St John.
The crash happened about 3pm on the Thames Coast road.
A St John spokeswoman said two patients received moderate injuries and one was seriously injured. All were transported to Thames Hospital.
The road is partially blocked and a tow truck has been called for both vehicles.