Portugal's centre-right ruling coalition has claimed victory in a national election after exit polls put it well ahead of the main opposition socialists, although likely shy of an outright parliament majority.

Polls show the government likely to win between 36.4% and 43% of the vote compared with 29.5-35% for the socialists.             

Two of the exit polls, by Catolica University for RTP television and by Intercampus/TVI, showed that the coalition could win a maximum of 116 to 118 seats in 230-seat parliament, while another showed a maximum of 108 seats.

That means it still has a slim chance of winning an outright majority.

"In the name of the coalition we are here to affirm that all the projections that are known point to a clear fact that the coalition Portugal Forward had a great victory on this election night," Marco Antonio Costa, deputy president of the main coalition party, the Social Democrats, told cheering supporters.

"We will maintain our commitment to guarantee a recovery ...and will maintain an attitude of dialogue."

The latest polls, released on Friday, gave Prime Minister Pedro Passos Coelho's ruling coalition a lead of between five and 12 points over centre-left Socialist opponent Antonio Costa.

But if Mr Passos Coelho, whose government introduced deep spending cuts and the biggest tax hikes in living memory, fails to secure more than the around 38% that he has polled in recent days, he will fall short of an absolute majority in the parliament.

The general election was the first since Portugal exited an international bailout last year.

In the last election in 2011, the two ruling parties together won 50.3% of the vote, securing them a stable majority government. The Socialists won 28% back then.

Partial results will start to trickle in during the coming hours but it may be some time before it is clear whether the government has obtained a majority.

Duarte Cordeiro, head of Socialist leader Antonio Costa's campaign, said that if the projections are confirmed, it would leave the Socialists short of their goal of forming a government themselves.

"If these results are confirmed, we believe that there is no parliamentary majority for any of the candidates in these elections," Mr Cordeiro said.

The formation of the government will then depend on President Anibal Cavaco Silva, whose duty it is to name the next prime minister.

However the constitution does not specify how the president picks the winner, whether by the number of votes or the number of lawmakers elected to parliament.