The men, two aged 24 and one aged 25, died when the white Toyota Hilux they were travelling in rolled on a gravel road about 25km from Lake King in the Eastern Wheatbelt region, 464km east of Perth, media reports said.
The Otago Daily Times understands the three were childhood friends who decided to move to Perth together several years ago.
They were believed to have been flatting together in Perth before Saturday's crash, the ODT was told yesterday.
The Perth Now website reported the single-vehicle crash was discovered early on Saturday morning.
Emergency services were called to the scene about 7.30am but arrived to find the men were already dead, the website reported.
Their names were yet to be released, but Dunedin police confirmed yesterday that one of the men was from Winton, a second was from Manapouri and the third from another part of Southland.
Police in those areas had been asked to tell next of kin in Southland of their deaths, Senior Sergeant Craig Dinnissen said.
A Western Australia police spokesman said he expected the names to be released today.
Family of the men were travelling from New Zealand to Perth to travel to the crash location.
The investigation into the circumstances surrounding the crash was continuing.
Further details on the investigation were expected to be released today, he said.