Search and rescue officials say the twin-engine plane was about 14 kilometres off the coast when it disappeared from radar screens around midnight Thursday night.
Search spokesman Lt. Edward Stanfield says the plane was on its approach to Sydney.
Stanfield says a coast guard auxiliary vessel was searching the area, but a mix of thunderstorms, low cloud and fog were hampering an air search.
A Cormorant helicopter from Gander, N.L., was en route, but a Cormorant and a Hercules aircraft were grounded in Greenwood, N.S., awaiting better weather.
Local fishing boats were also expected to join the search.
Early indications suggested the plane was a Cessna.
There was no word on the identities of those on board or the flight’s point of origin.