A St John spokeswoman said it was called to an incident at the intersection of North Rd and Northumberland St, in the suburb of North East Valley, about 4.10pm.
One ambulance and a rapid response vehicle treated one patient at the scene, who was then transported to Dunedin Hospital in a critical condition, she said.
A witness said the patient was a man who was hit by a truck. He was bleeding and bystanders were performing CPR before emergency services arrived.
A group of people were huddled around a truck driver who was visibly distraught, she said.
A Fire and Emergency New Zealand spokesman said two crews from Willowbank and Dunedin Central stations attended, helping with traffic management and patient care until an ambulance arrived.
Appeal for witness to come forward
Police confirmed they were called to a serious crash involving a vehicle and a pedestrian this afternoon and are appealing for a witness to come forward.
In a statement tonight, police said they were aware that a man in a silver vehicle spoke to the truck driver after seeing the crash and believed he could assist with the investigation.
"This man was not involved in the incident and police working to piece together the circumstances of the crash would appreciate any information he has.
"We encourage this person to please get in contact with police on 105 and quote event number P049865552."
North Rd was closed for a time, with diversions in place for northbound traffic in Islington St and southbound traffic in Blacks Rd.
Motorists were advised to avoid the area or delay travel.
A number of Fulton Hogan employees were seen talking to police earlier.
The police serious crash unit would visit the scene.
