The fire service, Gasco employees and police were called to The Junction building about 10.40am after a strong smell of gas was reported.
The building, on the corner of Gorge and Robins Rds, houses the Mediterranean Market, Bonisch Surveyors, A Touch of Spice, Control 4 and McKenzie and Willis.
About 50 people were evacuated from the complex, and neighbouring business Back on Track Physiotherapy voluntarily left their premises.
Drivers of cars parked outside the Mediterranean Market were advised they could not move their vehicles in case a spark ignited the gas. Police cars blocked Robins Rd, with a cordon formed near the Queenstown Fire Station, on the corner of Robins Rd and Isle St.
Another cordon blocked traffic at the intersection between Gorge Rd and Robins Rd.
Queenstown Primary School, on Robins Rd, remained operational throughout the callout, and it was also decided residences and visitor accommodation providers in the vicinity did not need to be evacuated.
"The concern is gas could seep downwards through the rest of the building and possibly reach the drains."
Queenstown Primary School was "OK", he said.
Three resort fire crews joined contractors from Gasco and all were stood down just before noon after the barbecue was found in what is understood to be a common room on the second storey of the building, which houses the Control 4 offices.
The incident controller, Senior Station Officer Grant Bewley, said the incident may have been caused by a barbecue "but that doesn't take away from the explosive problem that we've had".
The fire service had used water to suppress and disperse the gas and ensure nothing ignited.
"It was a great response ... there was no explosion," Mr Bewley said.
Gasco network manager Steve Norton said the company detected a "reasonable level of gas" when it was called.
"We couldn't ascertain where it [the smell] was coming from, but there was a barbecue ... in an enclosed room.
"It was basically a storage [cupboard] and the drain filled up with gas.
"The barbecue gas bottle was still attached and we have found that was leaking."
Mr Norton said the cause of the gas leak was unusual, but there was a lesson in it for everyone.
"The bottle was attached to the barbecue - to turn the bottle off, for a start, would be a good idea. Disconnecting the bottle would be a good, safe option and store it outside - it was in the middle of the building.
"It is absolutely bad practice to leave a barbecue inside ... it's a good [lesson]."
Control 4 managing director Tristan Franklin could not be reached for comment yesterday.
