A search is underway for a 69-year-old German tourist who was last seen on Saturday while hiking in the Mount Augustus area, about 850 kilometres north of Perth.

Key points: The man was hiking in the area with his wife when they became separated

The man was hiking in the area with his wife when they became separated Police and emergency service workers from Perth and around the region have joined the search

Police and emergency service workers from Perth and around the region have joined the search Searchers say temperatures on the ground on Sunday would have been in the mid-40s

The man set off on the hike with his wife on Saturday morning before the pair lost sight of one another.

She returned to the vehicle mid-afternoon, but became concerned when her husband did not return.

WA Police said the woman received help from other tourists in the area to try to find her husband, before authorities were notified.

Mt Augustus is about 2.5 times taller than Uluru. ( ABC Pilbara: Chris Lewis )

The Australian Maritime Safety Authority conducted an air search of the vast site on Saturday night and Sunday, with the Karratha Police Air Wing also travelling to the area to help with the search.

Searchers have told the ABC they expected temperatures on the ground to reach the mid-40s on Sunday "without a doubt".

Officers from a number of police stations in the region are involved in the search with State Emergency Service volunteers from around the region also joining the effort.

Volunteers prepare to fly from Perth to join the search. ( Supplied: WA Police )

Mount Augustus stands 2.5 times taller than Uluru, and is sometimes touted as the world's largest monolith, but many experts argue that is not the case because it is made up of multiple rock types.

The walk to the summit can take anywhere between five and eight hours, and the WA Department of Parks and Wildlife advises that climbers should have a "high level of fitness".