Opposition candidates said Sunday's Presidential poll in Comoros was marred by irregularities including barring of independent monitors and marking of ballot papers before voting began, charges rejected by the government.

About 300 000 voters in the Indian ocean archipelago of 800 000 people took part in the poll, with results expected to be announced by the electoral body CENI on Monday.

Incumbent Azali Assoumani, a former military officer, is widely expected to be re-elected from a field of 13 contenders.

"Election monitors for various independent candidates did not receive necessary accreditation documents to access the polling stations," the 12 opposition candidates said in a joint statement on Sunday.

Some polling stations had opened earlier than the official time while some ballot boxes were already filled, they said.

The opposition also accused authorities of arresting some of their representatives and preventing others from accessing CENI's premises.

Interior minister Mohamed Daoudou, who organised the poll, denied the opposition's claims.

"The poll took place in a calm and peaceful atmosphere," he said, adding voter turn out was 40%.

In the capital Moroni, groups of youths massed on main roads after polls closed in the early evening, erecting barricades and protesting against the alleged irregularities.

Last year Comoros was rattled by months of unrest as authorities moved to quell protests against Assoumani's bid to extend presidential term limits.

People on the archipelago's Anjouan island were angry that the move, which allowed Assoumani to participate in Sunday's poll, would deny them the presidency under a system that rotates the post among the country's three main islands.