Two Wānaka fire appliances, supported by one from Lake Hāwea, had extinguished the fire by 1am yesterday.
The fire did not spread to other mall businesses.
Wānaka fire chief Tony Wellman said he could not discuss the cause of the fire because the case was now with police.
A Fire and Emergency NZ communications shift manager said a fire safety investigator inspected the aftermath between 10am and 12.30pm yesterday and it was now a police investigation.
A police media spokesman said yesterday inquiries were ongoing "following a bin fire outside a commercial premises on Ardmore St".
"The fire was referred to police at around 10.20am, and the fire is reported to have occurred around 9.50pm [Sunday]."
When approached yesterday, the owners of the two businesses did not want to comment but permitted photographs of their damaged premises.
Green Toad, a snow sports and bike rental outfit first established in Queenstown in 1992, has been operating from Wānaka town centre for more than 20 years.
The next-door Japanese food outlet Sushi Mii was established more recently.
While the owners were reluctant to talk, they said they were grateful people from various nearby businesses noticed the fire, called 111 and turned hoses on it.
A Fenz communications centre shift manager said the fire appeared to have started in a rubbish skip and then spread to the adjacent building, where it began moving into the roof.
The shift manager said firefighters had to gain entry to extinguish the blaze.
