A Ballarat East woman has been missing for more than 24 hours after going for a run in the Canadian area of the Woowookarung Regional Park on Sunday morning.
The woman, identified by police as Samantha Murphy, 51, left her property on Eureka Street about 7am on Sunday and has not been seen since.
Her family, friends and police have sent out alerts.
The temperature rose to 36 degrees in the Ballarat region on Sunday, and police said this has informed the search due to the increased risk.
Ms Murphy's disappearance has been described as out of character, as she was familiar with the trails she intended to run.
Police have said she was well known to the local community and walked or ran in the area every day.
Ms Murphy's phone was on and with her when she disappeared, and police have been using phone data to help narrow the search.
Police, the SES, and Forrest Fire Management are searching both in the area near Ms Murphy's Ballarat home, and the forest area behind the Buninyong Golf Club, on foot, in vehicles, and by motorcycle.
A helicopter and drone have been deployed, with mounted units to join the search on Monday afternoon to help with reaching more difficult terrain.
Ballarat Police Acting Inspector Lisa Macdougall described the search grid as "extensive".
"Sam did go out every day, it was a regular habit of hers," she said.
"Our inquiries are such that we're going to look into all of the possibilities of where she might have gone."
Two SES volunteers are helping police to coordinate the search through a base at the Buninyong Police Station.
"We're all hoping for a positive outcome in the search for Samantha, and we thank our dedicated SES volunteers for their time," said VICSES Grampians duty officer, Jarrod McLean in a statement.
Ms Murphy is described as Caucasian, about 173 centimetres tall, of slim build and with shoulder-length blonde hair.
She was last seen wearing black exercise leggings and a brown singlet.
Police thanked the community members that had been coming forward to help with the search, and asked anyone who sees Ms Murphy, or has information on her whereabouts, to contact Crimestoppers, or triple-0.