Police say they have serious concerns for the welfare of a man with a medical condition lost in bushland northwest of Sydney after a fourth day of searching yielded no results.
Tiemuzhen Chalaer was last seen early on Sunday morning when he wandered into the bush near Wisemans Ferry with no supplies and no medication for his medical condition after a camping party.
Hawkesbury police Chief Inspector Garry Sims told AAP police are seriously concerned about Mr Chalaer due to his medical condition.
"We have very serious concerns for his health," he said on Thursday.
"The longer the time goes on the concerns for his welfare increase because of his exposure to elements and being there without food or water."
A team of 40 police officers and SES volunteers and a police dog have spent four days scouring bushland near the Wheelbarrow Ridge Road track in Lower Portland and will return on Friday morning.
The search party has broken the terrain surrounding the campsite into 17 search sectors, Insp Sims said.
"We are not necessarily expanding the search ... we believe we're in the right area. Because of the terrain, the gentleman's age, we don't think he's wandered too far."
Insp Sims said it was not uncommon for rescue parties to last this long.
Searchers will return to the area at 9am on Friday.
