Rescue crews are racing against the clock to find a Sydney man missing in the Blue Mountains before expected freezing temperatures and snow set in.
Gary Tweddle, from Cremorne on Sydney's Lower North Shore, was last seen in the early hours of Tuesday leaving the Fairmont Resort in Leura.
The 23-year-old had been at the resort for a work conference.
Police say he spoke to work colleagues on his mobile phone just after midnight and told them he was lost in bushland but was near a main road.
He was said to be in good spirits at that time.
Police say his phone either has no battery left or is switched off.
Detective Inspector Mick Bostock says weather conditions have been unusually mild over the past few nights, increasing Mr Tweddle's chances for survival.
But he says harsh conditions are expected to set in today.
"This afternoon a cold front is expected to move in," he said.
"Tomorrow it's forecast to snow, the temperature one degree, to a maximum of 5 degrees.
"It's important if he's going to survive that we find him before this cold weather comes in."
Detective Inspector Bostock says police have received multiple reports from the public.
"We have had a number of people come forward with information," he said.
"They've heard voices and coo-ee. We're not discounting any information, we're checking out all leads."
On Friday 75 officers and volunteers searched bushland near the Leura resort.
A police helicopter was used to conduct aerial searches and police divers surveyed dams at a nearby golf club.
"We're expecting to have about 150 volunteers from the Rural Fire Service, SES and Volunteer Rescue Association assisting us with the search," Detective Inspector Bostock said.
Mr Tweddle is described as 165 to 170 centimetres tall, medium build with brown eyes and brown hair.
He is thought to be wearing blue jeans, black jacket and checked shirt.
Anyone with information on his whereabouts is urged to call Crime Stoppers on 1800 333 000.