Eighteen people were taken to hospital after high levels of carbon monoxide were detected at a restaurant in Scarborough’s Golden Mile area.

Elevated levels of the poisonous gas were detected at the back of a Mandarin restaurant in the Eglinton Avenue and Birchmount Road area after a number of people reported feeling unwell Wednesday afternoon, Toronto Fire Services said.

Paramedics initially checked over seven people at the scene, but later said a total of 18 people were eventually taken to three separate hospitals to be checked out. Most of them are employees of the restaurant, paramedics said.

Commercial buildings are not required to have carbon monoxide detectors, so it wasn’t until firefighters arrived on scene that they were able to confirm the presence of the gas.

“There are acceptable levels (of carbon monoxide),” Acting Platoon Chief Colin Giffin told CP24 outside the restaurant. “This being a commercial establishment, acceptable levels would be anything under 25 (parts per million). The crews this afternoon were getting levels in the 500 to 600 parts per million. So that is exceptionally high and that will bring about symptoms from people quite quickly.”

The restaurant and an adjoining business were evacuated and the gas company was called to the scene to determine the source of the leak.

“As it stands now their investigation is ongoing and we don’t really know the source,” Giffin said.

There was no update late Wednesday on the condition of those transported to hospital.