Australia Post has apologised after delivering a postcard from Tahiti 50 years after it was sent.

A couple from Adelaide said they found the postcard from the French Polynesian island, which was dated 1966, in their letterbox, according to the Adelaide Advertiser.

The "slightly faded" postcard was addressed to "Robert Giorgio" and sent from "Chris", who said he was "enjoying myself greatly", despite the "very humid" weather.

The postcard showed a scene from the Papeete waterfront and the Bloc Donald building, which was featured on several postcards in the 1950s.

The stamp on the postcard cost 13 francs.

Tim Duffy, who found the postcard beneath a water bill, said he believed Giorgio may have been his property's original owner.

A spokesman for Australia Post told the Advertiser: "It is clear something went wrong 50 years ago after the postcard was posted in French Polynesia, and we apologise for the inconvenience.

"Australia Post takes great pride in the timely, safe and efficient delivery of mail, and we are confident that the vast majority of mail and parcels arrive on time."