Tired of patients, some critically ill, waiting in ambulances to be admitted to a hospital, medics protested by offering free transports for 24 hours.
The Ambulance Employees Association told ABC News that "ramping" has got to stop.
Union official Phil Palmer said although crews were promised that the delays would stop after the hospital's renovations were completed, that was not the case.
"There was an incident last night at the Flinders Medical Centre about 10:30, a fairly ill patient with a serious internal bleed was left outside for 40 minutes," he told reporters. "It was only one ambulance but that's just the straw that broke the camel's back."
The patient eventually got passed on to hospital staff by the ambulance crew after 57 minutes.
Another patient in an ambulance, designated as category 4, had an 11-minute wait outside because of an influx in the emergency department, according to the report.
South Australian Health Minister John Hill said an independent party would be brought in to look at emergency department problems at Flinders.