A man had to be restrained by six people, including police officers, after he attacked paramedics.
The Northern Ireland Ambulance Service (NIAS) said the incident, which happened on Saturday night in Newtownards, left the north Down area with reduced cover.
The ambulance staff were treated at the Ulster Hospital and were unable to continue their shift.
It was the second weekend in a row that paramedics were attacked in the area.
NIAS said paramedics responded to a 999 call for a man who was reportedly under the influence of drugs.
While being taken to hospital, he assaulted the paramedic in the back of the ambulance, who sustained back and shoulder injuries.
When the ambulance arrived at the Ulster Hospital in Dundonald, another crew came to help and the patient assaulted a further two crew members.
NIAS said it eventually took six people to restrain him before he was taken in to the emergency department.
Michael Bloomfield, NIAS chief executive, said he was “appalled”.
“We cannot provide our service if staff are taken off shift as a result of injuries sustained from assaults, and once again ambulance services in this area were considerably reduced last night as a result of this attack,” he said.
“These attacks are totally unacceptable and, while thankful for their support to date, I would appeal to parents, guardians, community leaders and others with influence to redouble their efforts in helping us protect our staff through engaging others on this issue.
“Once again, I would also re-iterate our view that those who commit such attacks should face the full rigour of the law, including custodial sentences.”