TWO experienced hikers have been found safe and alive after going missing in the Victorian Alps on Friday, sparking a massive hunt which lasted five days.

Trevor Salvado, 60, and Jacinta Bohan, 58, had set off on what was supposed to be a three-hour hike on Mount Buffalo on Friday.

It comes after the rescue mission was today scaled up on the fifth day of the search.

The area where they vanished is a rugged mix of bush and ravines.

There was speculation that one of them might have fallen into one of the ravines, and the other went in to help.

Large search crews today scourer walking tracks east of Lake Catani, after covering significant ground across other parts of the rugged mountain.

Senior Sergeant Damien Pepplar earlier said searchers were "optimistic" the couple would be found.

SON'S PLEA FOR MISSING PARENTS

Friends raised the alarm when they did not arrive as expected on Friday. The ­couple's car was found, near a large reservoir, about 3pm on Saturday.

The hunt for the couple, which initially focused on an area in a 500m radius of where their car was found, expanded on Monday, and the number of specialist searchers doubled.

Searchers have been using thermal night-vision technology, as well as GPS to ensure that every centimetre of the search zone is covered.

The couple's children, Nathan, 21, Issac, 23, and Rachel, 19, have gathered with family at the search post.

Nathan said the family remained hopeful that the "fit and responsible" couple would be found.

He said he wanted his parents to know how much he loves and misses them.

"I want them to know we are looking them and doing as much as we can to find them," Nathan said. "I just want them to be warm and safe."

The couple's other children, Isaac, 23, and Rachel, 19, have gathered with extended family members at the Mt Buffalo search post as rescuers scour the surrounding terrain.

Nathan last spoke to his parents on Wednesday or Thursday when they informed him they were going on a bush walk with their usual group of friends.

"A lot is going through my head," he said.

Cindy's older sister, Maria Bohan, said they were "staying strong".

"We are being tough … We hope they are safe and found very soon," she said.

The family thanked police and emergency services for their tireless efforts searching the mountain.

Nathan said his parents are both incredibly supportive and love the outdoors.

"They are funny. They believe in you. They are such nice people," he said.

He said his dad enjoyed riding, bushwalking and paragliding, while his mum was an avid gardener who dedicated time to volunteer community projects.

Inspector Joy Arbuthnot said about 120 people were involved in the alpine rescue operation.

Police were also making inquiries at the Bright campsite and the couple's home in Essendon.

SEARCH WIDENED FOR MISSING COUPLE ON MONDAY

Bush Search and Rescue Victoria spokesman Peter Campbell earlier said volunteers would begin searching off-track areas after covering off all formed tracks.

He added campers and rescuers had seen no sign of the couple since their disappearance on Friday.

The hikes on the mountain require very little experience, he said.

"We are here to find them and we will keep looking," he said.

The Westpac search and rescue helicopter joined the police air wing at the search zone.

"There are some tracks on the map that no longer exist," Mr Campbell said.

"The search area is being increased and we are also re-looking at some sights. A lot of tracks are for day walks … not a lot of experience is required."

Police on the scene have described the couple's disappearance as "strange" and have vowed to continue searching for the missing husband and wife.

Sergeant Martin Torpey described the husband and wife as experienced hikers who had been coming to the Mount Buffalo area for almost a decade.

Sgt Torpey said the terrain was made up of boulders and thick bush.

"It's quite treacherous and there are some ravines with a steep drop," he said.

"We think one may have fell and the other has gone down to help them. It's rare that two would go missing."

GPS trackers have been fitted to those scouring the terrain to make sure all areas have been covered.

A major search for the pair on Sunday focused on a "treacherous" 500m radius zone close to where the couple's fawn coloured Skoda Yetu (rego 1AN 6RT) was parked.

A large reservoir is located nearby and a bag containing clothes were found in the vehicle, located about 3pm on Saturday.

FRIENDS' HOPEFUL WAIT FOR COUPLE'S RETURN

Friend Sav De Vuono, along with her husband Mario and two other couples, remained at the campsite where they waited for Trevor and Cindy to return over the weekend.

"The type of people they are, they're fighters, they're out there and they know what they are doing, so we can't understand it," Mrs De Vuono said.

"He's an ex-pilot, he just retired in December, so he's pretty switched on and just a barrel of laughs, he's an amazing guy.

"Cindy works in community health and transition into schools, she's a schoolteacher by trade.

"They both do a lot of hiking, they've done a lot of things more dangerous than going for a walk, and Cindy, she just got back from New Zealand doing a hike there."

Mrs De Vuono said despite their kids getting older and no longer coming on the camping trips, the four couples still loved the annual get-together.

"We've been here for nine years, nothing changes," she said. "It's just out of control."

SES volunteers were guarding the entrance of Mount Buffalo and showing drivers an image of the missing couple in the hope someone might know more about their whereabouts.

Dozens of SES, bush search and rescue and police members also scoured the ground, as a police chopper searched from above.

The mounted branch and motorcyclists was also involved.

SES deputy controller Graham Gales said crews were "climbing and looking under every rock".

aneeka.simonis@news.com.au