Police have "serious concerns" for the wellbeing of a man missing from a Dunedin hospital since Thursday afternoon.

About 50 LandSAR volunteers and police are searching for Gordon Mclean, also known as "Gordy", who left Wakari Hospital, Taieri Road, Dunedin about 3pm.

They've searched the Wakari, Helensburgh , Halfway Bush and Kaikorai valley, but have been unable to find him or any clues as to where he may be.

The 63-year-old was considered very frail and police have serious concerns for his welfare and fear he may have fallen, Sergeant Richard Panting said.

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He is about 152cm tall, of very thin build.

He was last seen wearing a dark-coloured polar fleece and trousers, and a red-coloured polo shirt. He had brown slippers on and a black puffer sleeveless jacket.

Police were concerned Mclean may have fallen and asked residents to check their properties - including sheds and outbuildings as he may have taken shelter - thoroughly, particularly in the Halfway Bush area.

Police asked anyone who thought they'd seen Mclean to report it to police immediately.