A video has been posted on their Facebook page, along with an appeal for clues to his identity.
"...We want to talk to this man who stopped the fire. If you know who this brave witness is please let us know," the post accompanying the video said.
The fire, which was believed to be deliberately lit, was in an alley adjacent to the Base Backpacker Building on Shotover Street, Detective Sergeant Brian Cameron said yesterday.
Two Queenstown fire department appliances attended the blaze and a scene examination was conducted by police.
Nobody was injured, but there was some property damage.
An Australian man has been arrested.
Anyone with information should contact Queenstown police on 03 441 1600 or send a personal message on Facebook.
