Chile's blanket ban on abortion will be eased after the constitutional court voted to allow terminations in some circumstances.

Previously one of seven Roman Catholic countries with a blanket bar on abortions, the new law says the procedure is justified after rape, if the mother's life is at risk or if the foetus is not expected to survive the pregnancy.

The current law was introduced in 1981 under the military rule of General Augusto Pinochet and the court's 6-4 ruling comes after more than two years of debate in the Chilean Congress. The Senate finally approved the bill last month but a last ditch effort by conservatives challenged its constitutionality arguing it failed to fulfill the constitution's requirement to 'protect the life that is about to be born.'

Attempts to ease the ban have been ongoing since 1991 but it has been held in place with support from the church and conservatives.

Abortion remains deeply controversial in the heavily Catholic country, despite winning support from President Michelle Bachelet and 70 per cent of the population.

The centre-left politician and former chief of UN Women Bachelet hailed Monday as an 'historic day for the women of Chile!' and tweeted 'we advance a basic right for our dignity'.

Americas director at Amnesty International, Erika Guevara-Rosas, said: 'Chile has finally moved one step closer to protecting the human rights of women and girls.'

But Chile's Catholic bishops said the bill 'offends the conscience and common good of our citizens'.

A statement from the Roman Catholic conference of bishops in Chile said: 'We are before a new situation in which some unborn human beings are left unprotected by the state in this basic and fundamental right.'