The bodies of a Norwegian woman, a British man and a German woman, were found in a burned-out car south-east of Perth, according to reports.
A farmer also lost his life trying to warn residents of the fire.
It was the first deadly bushfire of the Australian summer, sparked by lightning.
The three European workers reportedly drove away from the property to rescue a horse and took a wrong turn into the fire.
Linda Campbell told the West Australian that all three victims worked for her on the property at Scaddan.
“If they had turned right at the gate and not left they wouldn’t have died,” she said.
“They had become part of the team and all the staff are taking this very hard.”