A search was last night mounted at Lake Te Anau after several flares were sighted.
Police said the flares were observed near the southern end of the lake at about 11pm.
"A number of police staff, volunteers and local tourist operators assisted in an extensive search of the lake, using marine craft and a helicopter to locate any possible persons in distress," a police spokesperson said.
Nothing of interest was located during the search.
Police are now appealing for anyone with information to come forward so they can establish the circumstances behind the flares being set off.
Any information should be given to the Te Anau police on 03 249 7600.