Victoria Police have conceded they hold “significant concerns” for missing Ballarat woman Samantha Murphy, as the search for her enters its sixth day.

In a significant shift on Friday, specialist detectives from the missing persons’ squad joined about 40 local police and dozens of volunteers searching for the 51-year-old mum of three.

Murphy has not been seen since she left her home in Eureka Street, Ballarat East, about 7am on Sunday to go for a run.

On Friday, search crews expanded their focus to the Buninyong area, after working through the Eureka and Canadian state forest areas.

But despite the widespread search, police have struggled to make any breakthroughs. Shortly before midday on Friday, the missing persons’ officers – who are experienced in investigating disappearances and conducting complex bushland searches – were brought in.

Officers refused to say if they believed Murphy was still alive, or if there were suspicious circumstances in her disappearance.

“We haven’t ruled out anything – the focus is finding her,” Victoria Police Inspector Bob Heaney said.

“We are in day six of the search. Our concern is heightened the longer the time goes.”

Detective Acting Superintendent Mark Hatt from Victoria Police’s Crime Command said there were major concerns for Murphy, but “nothing immediate to indicate there is anything sinister behind [her] disappearance”.

Homicide detectives are not involved in the search.

“We still have a number of avenues of inquiry to pursue, and the search to try and locate her is ongoing today,” Hatt said.

“I also think it’s important that people avoid unnecessary and unhelpful speculation. However, it is especially concerning that we have now gone six days without any contact from her or any potential sightings.

“We do hold significant concerns for Samantha’s welfare at this stage and that is growing as the day progresses,” he said.

Hatt said police were working with IT specialists to try to find out where Murphy went when she left her home. She is thought to have taken her phone and a smartwatch with her, although police have not said if those items have yielded any information.

Heany said Murphy’s movements on Sunday morning were fairly typical.

“Samantha’s very fit – both physically and mentally – she would cover up to 14 to 15 kilometres on her runs,” he said.

“She’d normally be due back from her run within a couple of hours, and alarm bells went up when she didn’t return.”

Earlier, police said they had ruled out CCTV released on Wednesday that was initially thought to have shown Murphy running on Eureka Street. It actually showed someone else.

Heany again appealed for residents in surrounding suburbs to review their CCTV footage for any sign of Murphy.

“One of the challenges we have is the area is so remote that there’s not a lot of businesses or residential CCTV available,” he said.

Search crews have canvassed a large area of Ballarat looking for the mother of three, with State Emergency Service and Country Fire Authority personnel helping police.

The local community has also helped. Volunteers on foot, riding bicycles, on horseback or in four-wheel drives have spent days picking through scrub and along roadsides.

On Thursday, Murphy’s distraught eldest daughter Jess called for help to bring her mother home.

“I know she’s out there somewhere, so if you could please continue to search for her to give us something to work with, we’d really appreciate it,” she said.

Murphy’s husband Mick added: “People just don’t vanish into thin air. Someone has got to know something.”

Anyone with information about the disappearance should contact Crime Stoppers.

– AAP