A man found in an empty housing estate with burns over most of his body is believed to have sustained his injuries in a fire in a portable toilet.

The 65-year-old Harrisdale man has been identified by WA Police after a public call for assistance.

The incident occurred on Nikon Road in Harrisdale about 3pm yesterday afternoon, police said.

Despite his injuries, the man walked several hundred metres from the toilet to an empty house on Glenora Way, where he was found by two tradesmen.

He was taken to Royal Perth Hospital, where he remained this afternoon in a critical condition.

Detective Senior Sergeant Tom Mills of Major Crime described the man's injuries as "horrific".

"He's in a very very dangerous position as far as his health goes... they are the most horrific burns I've seen," he said.

Police are urging anyone who may have seen the man to contact Crime Stoppers.

"[We're appealing to] anyone who might have been in that area," Detective Mills said.

"Other tradesmen who may have been working, although it was a public holiday, people who are building ... and may have been looking at the progress of their new homes, anyone who saw a man wandering around."