Pakistan's Supreme Court on Wednesday freed a Christian woman from a death sentence for blasphemy against Islam and overturned her conviction, sparking angry protests and death threats from hardline religious.

New Prime Minister Imran Khan issued a warning to the religious right late in the evening that any prolonged blockade of streets would be met with action.

Asia Bibi, a mother of four, had 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 neighbors objected to her drinking water from their glass because she was not Muslim. Bibi has always denied committing blasphemy.

Chief Justice Saqib Nisar, who headed a special three-judge bench set up for the appeal, cited the Koran in the ruling, writing that "tolerance is the basic principle of Islam" and noting the religion condemns injustice and oppression.

In overturning her conviction, the ruling said the evidence against Bibi was insufficient.

Bibi did not appear in the courtroom and her whereabouts were a closely held secret for fear of attacks on her and her family. Many have speculated they will be forced to leave the country, but there was no confirmation of their plans.

Her lawyer called the court ruling "great news" for Pakistan.

"Pakistan's Supreme Court must be appreciated that it upheld the law of the land and didn't succumb to any pressure," her lawyer Saiful Mulook said.

The ruling was immediately met with street protests. Major roads were blocked by mid-afternoon, paralyzing parts of Islamabad, Lahore and other cities.

Khan addressed the nation in a televised speech on Wednesday night, supporting the court ruling and warning the ultra-Islamists not to disrupt the nation.

"We will not allow any damages to occur. We will not allow traffic to be blocked," Khan said. "I appeal to you, do not push the state to the extent that it is forced to take action."