Ahmed Abdallah Sambi has won weekend presidential polls in Comoros, the secretary of state for elections says.

Ali Abdallah, who is in charge of announcing the election outcome, said on Monday that Sambi had won.

The official result is expected on Tuesday.

Abdallah said the final results from Sunday's vote would not change the overall trend.

"That is to say Sambi is the winner," he said.

Officials were expected to announce the final results on Monday night but Abdallah said this had been delayed because envelopes from some voting bureaus had been sent to the wrong place in the Indian Ocean archipelago.

Sambi beat retired French air force officer Mohamed Djaanfari and long-time politician Ibrahim Halidi, whose candidacy was backed by Azali Assoumani, the outgoing president.

Sambi, 48, a cleric and successful businessman educated in Iran, Saudi Arabia and Sudan, was the favourite due to his strong showing in an April primary on Anjouan island that winnowed the field from 13 to three candidates.

Considered a moderate, he has spoken in support of an Islamic government on the impoverished, overwhelmingly Muslim archipelago.

PHOTO CAPTION