Rescue crews hold “serious concerns” for a bushwalker who has been missing for almost a week in waist-deep snow and icy conditions.

Tasmanian man Daryl Fong had set out on a day hike in the Mt Field National Park area, about 60km north-west of Hobart, last Saturday morning.

The last known contact was about 3am on Sunday when he texted a friend, advising that he had been delayed and intended to seek shelter and camp in the park overnight.

The 30-year-old’s friend contacted the police on Monday, concerned about Fong’s welfare, leading to search crews deploying later that day.

Crews are focusing on the Tarn Shelf area on Friday, Tasmania Police Inspector Luke Horne said.

“Over the past days, search teams have been faced with difficult conditions in the area, including waist-deep snow, poor visibility, and near gale force winds,” he said.

“We remain committed to finding Daryl but with the passing of time and the conditions in the area, we hold serious concerns for his welfare.”

The Tarn Shelf area includes a 12km walking circuit that features a series of small glacial lakes, with the tarns often frozen in winter, and has short, steep hills, rough surfaces and many steps, according to the Tasmanian Parks and Wildlife Service.

Police search and rescue, State Emergency Service, and wilderness paramedics have been deployed, with a rescue helicopter also called in to help in previous days.

Fong’s car, a white Subaru, was found in the Lake Dobson carpark, where he left it when he began his walk.

Horne said there’d been about 100 people in the Mt Field National Park area since Fong set off.

He urged those people to contact Bridgewater Police if they’d  seen Fong’s vehicle in the carpark, and anyone else, or if they have any information relating to his movements.

Mount Field National Park, one of Tasmania’s oldest, is home to a diverse array of alpine vegetation, ranging from tall eucalypt forests to glaciated landscapes and cascading waterfalls.

Search crews are also continuing to look for 76-year-old Peter Willoughby, who went missing in Hollybank Forest Reserve in north-east Tasmania.

The Scottsdale man, who has a medical condition that can cause him to become disoriented, was reported missing on October 5 after he and others tried to retrieve his bogged station wagon from a rural road.

Police hold serious concerns for Willoughby’s welfare and the potential for hypothermia, with heavy rain having lashed the region.

Several hikers have died in recent months after getting into trouble in freezing conditions in south-east Australia.

The bodies of two women were discovered in an alpine hut by a pair of bushwalkers on October 3, north-east of the popular Falls Creek ski resort in Victoria.

A tourist from China who was walking with a group in Tasmania’s Cradle Mountain National Park died in late September after becoming overwhelmed by cold weather.

–AAP