Eastern Health said the incident occurred when the ambulance had to stop along the Trans Canada Highway in St. John's because of the person's condition.
The health board says the patient left the vehicle after it pulled over and ran into a wooded area.
An RCMP spokesman says the ambulance crew called the Royal Newfoundland Constabulary just after 12:30 a.m. and asked for assistance in finding the patient.
"The RNC showed up and they had a dog as well, and they were trying to track this person down and couldn't find the person," said RCMP Sgt. Marc Coulombe.
Coulombe says the Mounties received a call at about 2:15 a.m. saying a person had been struck and killed by a vehicle on the highway.
Coulombe says the man was hit by a transport truck in the east bound lane of the Foxtrap access road.
Conditions were reported to be raining and foggy at the time of the accident.
The health board says it is reviewing what happened.
The victim's name has not been released.
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