Pakistan's Supreme Court on Wednesday overturned the conviction of a Christian woman sentenced to death for blasphemy against Islam and ordered her freed, a ruling that set off protests by hardline Islamists but was welcomed by human rights advocates.

Asia Bibi, a mother of four, has been living on death row since 2010 when she became the first woman to be sentenced to death by hanging under Pakistan's draconian blasphemy laws.

She was condemned for allegedly making derogatory remarks about Islam after neighbours objected to her drinking water from their glass because she was not Muslim.

She has always denied blaspheming.

News agency AFP said Asia Bibi could scarcely believe the news:

'I can't believe what I am hearing,' she said. 'Will they let me out, really? I just don't know what to say, I am very happy, I can't believe it.'

Her husband Ashiq told AFP: 'I am very happy. My children are very happy. We are grateful to God. We are grateful to the judges for giving us justice. We knew that she is innocent.'

Her case has outraged Christians worldwide and been a source of division within Pakistan, where two politicians who sought to help her were assassinated.

Release International, which supports persecuted Christians around the world, describes the ruling as a triumph, and is now calling for Asia, her family and her lawyer to be protected from vigilantes who may try to take the law into their own hands.

'We welcome this verdict,' said Release chief executive Paul Robinson. 'Finally humanity and common sense have triumphed over extremism. Asia was falsely accused because she was a Christian. Pakistan must act to protect the lives of this mother, her family and her lawyer. And Pakistan must take immediate action to repeal these notorious blasphemy laws, which are being used as an instrument of persecution against the country's Christian minority.'

The British Pakistani Christian Association's officer in Pakistan, Mehwish Bhatti, said: 'We are so happy and thankful to God for this big day! All glory goes to Him. The decision was tough; God has strengthened the resolve of the Justices and has made it possible. I pray for the peace of minorities, let God be their guardian.'

BCPA chairman Wilson Chowdhry said: 'Asia Bibi has endured almost 10 years of brutal incarceration in isolation. The world has watched her suffer but today thanks to the grace of God today the world rejoices.

'Her freedom can hardly be called justice and nothing will ever compensate her for her lost years.

'For now we can only pray that she is given the counselling and support she needs to recover and restore her place in society – this will of course be in a nation far away from Pakistan where it is untenable for her to remain.'

He added: 'Pakistan is increasingly exhibiting an intolerance to non-Muslims that has to be tackled by it's government. That extremists can induce riots and bring the country to a standstill is bewildering.

'We call on the Government of Pakistan to assure Christians of their safety during these tumultuous times, moreover we call for people to pray for a restoration of peace in a nation that is riven by fundamentalism.'

Supporters of Islamist political party Tehreek-e-Labaik (TLP), which was founded to support Pakistan's harsh blasphemy laws, immediately condemned the ruling and blocked roads in Karachi, the country's largest city, and in the city of Lahore.

It called for the death of the chief justice of the Supreme Court and two other judges who overturned the death sentence and for the ouster of Prime Minister Imran Khan's government over the case. 

'The patron in chief of TLP, Muhammad Afzal Qadri, has issued the edict that says the chief justice and all those who ordered the release of Asia deserve death,' said party spokesman Ejaz Ashrafi.

Chief Justice Saqib Nasir, who headed a special three-person bench set up for the appeal, cited the Quran in his ruling, writing 'Tolerance is the basic principle of Islam' and noting the religion condemns injustice and oppression.

'It is great news for Pakistan and rest of the world,' Asia Bibi's lawyer Saiful Mulook told Reuters. 'Asia Bibi has finally been served justice. ...Pakistan's Supreme Court must be appreciated that it upheld the law of the land and didn't succumb to any pressure.'

The case has been high on the agenda of religious hardliners in Pakistan, many of whom are fiercely opposed to her release.

In November, TLP staged a crippling blockade of the capital, Islamabad, after small changes to a religious oath, which it claims was tantamount to blasphemy. Seven people were killed and more than 200 wounded in clashes with the police and TLP's supporters only dispersed after striking a deal with the military.

Insulting Islam's prophet is punishable by death under Pakistani law, and blasphemy accusations stir such emotions that they are almost impossible to defend against. Dozens have been killed following blasphemy claims, sometimes by mobs of men.

Rights groups say the blasphemy law is exploited by religious extremists as well as ordinary Pakistanis to settle personal scores. The law does not clearly define blasphemy and evidence might not be reproduced in court for fear of committing a fresh offence.

Asia Bibi's representatives have claimed she was involved in a dispute with her neighbours and that her accusers had contradicted themselves.

In February, her husband Ashiq Masih and one of her daughters met with Pope Francis shortly before Rome's ancient Colosseum was lit in red one evening in solidarity with persecuted Christians, and Asia Bibi in particular.

Pope Francis told her daughter: 'I think often of your mother and I pray for her.'

Christians make up only about two per cent of Pakistan's population face severe discrimination.

'This is a landmark verdict. For the past eight years, Asia Bibi's life languished in limbo,' said Omar Waraich, deputy South Asia director for Amnesty International.

'The message must go out that the blasphemy laws will no longer be used to persecute the country's most vulnerable minorities.'

Asia Bibi has been offered asylum in several countries and was expected to leave the country if acquitted.

Additional reporting by Reuters.