A police spokeswoman said the accident occurred on a farm in Mataura Island-Titiroa Rd, Mataura Island, about 2pm.
An Otago Regional Rescue Helicopter was dispatched from Dunedin to assist the patient.
Fire and Emergency New Zealand shift manager Lyn Crosson confirmed crews from Tokanui, Waimahaka and a medical first responders team from Edendale were sent to the scene.
St John spokesman Gerard Campbell said one patient had been flown by helicopter to Dunedin Hospital with critical injuries.