Emergency services were continuing to search a mountainous part of Co Kerry last night after receiving reports that an aircraft had crashed in the area.
The search resulted from a call to the Garda from a witness on the Dingle Peninsula who saw smoke trailing out of the back of the light aircraft at about 6.20 p.m.
A local man, Mr Damien Duffy, said he saw the aircraft crash into the side of Strickeen Hill, near the village of Lispole. Another witness reported seeing smoke billowing in the area, and a third person heard a number of loud bangs.
The Shannon Coast Guard helicopter, gardaí, firefighters from Dingle and Tralee and the Kerry mountain rescue team joined the search, which was initially concentrated on an area between Lispole and the nearby Connor Pass.
The lifeboats at Fenit and Valentia were placed on standby.
The weather was excellent at the time of the reported crash. However, fog moved into some areas later, compounding the difficulties faced by rescuers working in steep terrain.
As night fell at about 8.30 p.m. and no sign of the aircraft was found, the Coast Guard's helicopter was withdrawn to Shannon for refuelling, and the main focus of the search effort moved farther up the Connor Pass.
A spokeswoman for the Irish Aviation Authority said it had no reports of missing aircraft and had received no distress signals. Farranfore is the only major airport in the region.
One theory being considered last night was that the aircraft was a micro-light.
The same area of west Kerry was the scene of a crash almost exactly a year ago, in which an experienced pilot was killed when the helicopter he was flying crashed in heavy fog.
The privately-owned Bell helicopter was en route from Weston Airport, Co Kildare, to Tralee when it hit a mountainside near Lispole, six miles from Dingle. The helicopter was due to pick up passengers from the Tralee races.
It is believed the pilot lost his bearings as heavy mists engulfed the helicopter.