The explosion at Italian restaurant Les Tilleuls near the centre of the Swiss city happened in the middle of the lunchtime rush, with the alarm going off at 1.18pm, rescue services captain Frederic Jaques told AFP.
"It appears to have been an accident. A small gas canister exploded," he said, adding that Geneva forensic police were investigating the cause of the explosion.
The exploding canister had been attached to a small blowtorch used to make crème brûlée and similar desserts.
"The volume of gas was quite small, but the blow-back effect was impressive," Jaques said.
The kitchen area had been completely destroyed, and two people working there at the time of the explosion had suffered burns.
The restaurant's windows were meanwhile blown out, spewing glass across a crowded terrace.
In all, 15 people were injured, including eight who were sent to hospital, Jaques said, adding that no one had suffered life-threatening injuries.
A full 21 firefighters and other rescue workers, in 12 vehicles, took part in the operation to secure the area and five ambulances also rushed to the scene.
Jaques said accidents involving exploding gas ca;nisters happened from time to time, but that they were rare in a restaurant setting.