Portugal's prime minister has promised to ease strict abortion laws in the conservative, Roman Catholic country, even though his government's proposal to scrap restrictions failed to win complete endorsement in a referendum Sunday.

With more than 99 per cent of votes counted, about 60 per cent approved the proposal allowing women to opt for abortions up to the 10th week of pregnancy. Just over 40 per cent opposed it.

Under Portuguese law, however, more than 50 per cent of the country's 8.9 million registered voters must participate in a referendum to make it valid. The turnout Sunday was 44 per cent.

Prime Minister José Sócrates, leader of the Socialist party, said he was undeterred by the low turnout and would stick to his pre-ballot pledge to change legislation.

"The people have spoken and they have spoken in a clear voice," he said.

The result "reinforced the political and legislative legitimacy" of his plans to change the law, he said.

Luís Marques Mendes, leader of the main opposition Social Democratic party, said he would not stand in the way of granting abortion rights through the 10th week, despite opposing it during campaigning.

Vote should be 'democratically respected': opposition

"Even though the [referendum] result is not binding, we believe it should be democratically respected," he said.

The Socialists' efforts to introduce more liberal laws, which failed nine years ago when a referendum on the same question drew a turnout of only 32 per cent, have faced emphatic opposition from the influential Roman Catholic church.

Church officials made no immediate comment on the referendum.

Portugal, where more than 90 per cent of people say they are Roman Catholic, has long had one of the most restrictive abortion laws in the European Union. Its current legislation places it in a minority in the bloc with Poland, Ireland and Malta.

In Portugal, the procedure is allowed only in cases of rape, fetal malformation or if a mother's health is in peril, and only in the first 12 weeks of pregnancy.

In the 23 other EU countries, abortion is permitted within much broader limits. Women can ask for abortions up to the 24th week of pregnancy in Britain and up to the 12th week in Germany, France and Italy.

Sócrates, whose party took power in a landslide victory almost two years ago after he promised broad reforms and modernization, described Portugal's law as "backward."

The law merely drives abortion underground, he said. Women seeking to terminate their pregnancies travel to EU countries where it is legal, especially private clinics across the border in Spain where abortion is permitted on psychological grounds, or resort to shady, back-street clinics at home.

Abortion rights campaigners said about 10,000 women are admitted to hospital every year with complications arising from botched back-street abortions.

"Portugal will now tackle abortion in the same way as most other developed European countries," Sócrates said.

However, women seeking an abortion will first have to go through counselling, "so that the decision is a considered one, not taken out of desperation," Sócrates said.

It could be several months before women can choose to terminate their pregnancies. A bill would have to be voted on and then go to the president for approval. It would come into force only when the new legislation is published in the public records, a procedure which usually takes months.