The people became ill after eating at The Copa Brazilian Churrasco restaurant in Dickson during the weekend.
The customers were treated for symptoms of salmonella poisoning, including diarrhea, stomach cramps and fever.
Hospitals called in extra staff to deal with the outbreak, the Australian Broadcasting Corp. said.
"It's put a lot of stress on the emergency department. The emergency departments of both hospitals have been extremely busy over the last month so to have something like this really tests that system," Australian Capital Territory Health Chief Health Officer Dr. Paul Kelly said.
Kelly said health investigators are working with the restaurant's staff to identify the cause of the illnesses.
"The issue with this particular restaurant being buffet style is that pretty much everyone ate everything," he said.
Health officials are investigating a second, unrelated food poisoning outbreak at an undisclosed restaurant in the same area.
About 60 patrons of that restaurant have come down with a mild form of gastroenteritis.
Both restaurants are closed, the ABC reported.