The man fell ill on Sunday afternoon and suffered from excruciating muscular seizures in his back, his sister Jane Stevens - his legal guardian - said.
The man had to wait outside for the ambulance to arrive and was very cold when it finally reached his home, Ms Stevens said.
"I don’t think anyone should be left sitting outside in the dark for 2½ hours ... he was in extreme pain... it is at level 10, and for an intellectually disabled man who doesn’t have a full understanding of what is happening to him, I am left gobsmacked that they could consider him non-urgent... he cannot be moved because that makes it worse."
St John Coastal Otago territory manager Doug Third said the call relating to the man was received at 4.54pm and his case was assessed as non-urgent.
"The patient was put through for a secondary, more comprehensive assessment by our 111 Clinical Hub where St John registered nurses and paramedics determine the best treatment for the patient by using a phone triage system," Mr Third said.
"While it is always our objective to respond as soon as possible with an ambulance if required, life-threatening calls are given the highest priority and at the time ... all our ambulances in Dunedin were responding to other jobs."
Ms Stevens said she accepted a critical case should be given priority, but said people with her brother had become increasingly frustrated at his not receiving the care he needed.
"How ill do you have to be to be considered an urgent case?
"I get that if you are in the midst of a heart attack or something completely life-threatening that you should take precedence, but ... it is not acceptable that our emergency service is providing this level of care for people who have an emergency, whatever the reasons for that."
Mr Third said a clinical support officer made two welfare checks on the patient.
"At 7pm, we were advised that the patient’s condition had changed, and an ambulance was dispatched, taking him to Dunedin Hospital in a moderate condition.
"St John takes patient welfare very seriously and would encourage the patient to be in direct contact with us if he is not satisfied with his treatment or care."
