Portugal's parliament is on Friday expected to pass a law allowing medically assisted dying, making the Catholic-majority country the fourth in Europe to legalize euthanasia.

Lawmakers approved proposals aimed at changing the law in February, setting up the vote despite a campaign by the Church for a national referendum on the issue.

The bill legalises access to assisted suicide for adult patients in a situation of "extreme suffering and irreversible damage".

Doctors and psychiatrists must validate the decision if the patient's ability to make a "free and informed" choice is in doubt.   

The vote, expected around midday, will take place behind closed doors because of coronavirus restrictions.

Any new bill must then be signed into law by recently re-elected president Marcelo Rebelo de Sousa, a staunch Catholic and conservative who has not publicly taken a position on the issue.

He could choose to veto the law, although a second vote by lawmakers would override the it.

"People deserve the right to be able to choose," said retired oncologist Jorge Espirito Santo, who has campaigned for years to make euthanasia legal.

He added he was expecting a "historic day".

The Catholic Church, which predominates in Portugal, campaigned against the draft bills both among its faithful and those of other denominations.

"The Church's position has not changed," spokesman for the Portuguese Episcopal Conference, Father Manuel Barbosa told AFP.

"Of course we hope that this law will not be approved." 

Euthanasia is legal in three European countries -- Belgium, The Netherlands and Luxemburg -- while others allow terminally ill people to refuse life-maintaining treatment or to have help to die.

In December neighbouring Spain's parliament voted by a wide margin to approve a bill that will allow euthanasia under strict conditions, despite fierce opposition from the Catholic church and conservative parties.