Police in Canada say they do not have any leads in the case of an Australian nuclear scientist who has been missing since mid-January.

The sudden disappearance of Lachlan Cranswick, 41, has mystified his colleagues.

Mr Cranswick was last seen on January 18 when he left work at a high security nuclear facility in Chalk River, in northern Ontario.

The facility produces about a third of the world's medical isotopes.

Police say Mr Cranswick's home was reportedly left unlocked and his car was in the garage.

His wallet, keys and passport have all been accounted for.

Colleagues did not notice anything strange about his recent behaviour.

One described him affectionately as a "safety-conscious nerd" who never went anywhere without his mobile phone and GPS.

Local police have said he was an avid hiker and photographer but a search of the nearby ski trails and forests has not turned up any clues.