Police are asking the public for help as the search for missing Omarama man Rodney Murdoch enters its sixth day.
Mr Murdoch, 71, was last seen at Omarama at about 9:30am on August 6.
He is believed to be driving a green/silver 1994 Toyota Hilux Surf, registration number CHW194 and is thought to have his grey and white giant schnauzer dog with him.
Constable Nayland Smith said Mr Murdoch had several health issues including early onset dementia and would be unable to take more than a few steps from the vehicle without the assistance of a walking aid.
"If we can find the vehicle then I believe we will be able to find Rod," Const Smith said.
Search and rescue crews and volunteers had spent about 480 hours scouring a large part of the South Island looking for Mr Murdoch since he went missing last week.
"We've pretty much covered the entire Mackenzie Basin. We've been as far as Temuka and down through Kurow searching all the back roads through to Oamaru. SAR teams have also searched Dunedin, there are areas of interest there like the peninsula. We've also covered the coastline from Oamaru to Warrington but found nothing," Const Nayland said.
Aerial and ground searches of all lakes, rivers and canals in the Mackenzie area have been made as well as a search over Lake Hawea.
"If he is trapped in the car somewhere we have real concerns for him with the sub-zero temperatures this week."
Police are asking all motorists in the area to keep an eye out for the vehicle and all landowners across the central and lower South Island to check their properties and farm buildings for any sign of Mr Murdoch.
Anyone with information on the whereabouts of Mr Murdoch should contact their local police station.