Pakistan has executed a former police bodyguard who killed the Punjab province governor over his call to reform strict blasphemy laws, in what was one of the country's most high-profile assassinations.

Street protests broke out within hours by supporters of the killer, who consider him a hero for defending the faith. The head of the Islamabad Bar Council called for a day-long strike of lawyers in protest against the hanging.

Mumtaz Qadri was working as a bodyguard for Salman Taseer, the governor of Punjab province, when he shot him dead in Islamabad in 2011. The governor was a vocal critic of Pakistan's harsh blasphemy laws, which stipulate a mandatory death sentence for anyone who insults the Prophet Muhammad.

"Qadri was hanged at around 4.30am," senior police officer Rizwan Omar Gondal said. The execution took place in the city of Rawalpindi outside Islamabad.

After his arrest, Qadri told police he killed Taseer because the governor had championed the cause of a Christian woman sentenced to death in a blasphemy case that arose out of a personal dispute. Taseer had said the law was being misused and should be reformed.

Qadri's attorney said his client told him he had no regrets for killing the governor.

"I have met him twice in jail. He said that even if Allah gave me 50 million lives, I would still sacrifice all of them," said lawyer Ghulam Mustafa Chaudhry.

Protesters block a road leading to Islamabad in protest at the execution of Mumtaz Qadri. Photo by Sohail Shahzad/EPA

Protesters briefly blocked the main road between Rawalpindi and Islamabad on Monday after news of the hanging broke. Police later dispersed them and closed off the road to prevent more demonstrations.

Chaudhry predicted larger demonstrations coinciding with Qadri's funeral, which his legal group said would be held on Tuesday.

"From what we are seeing, this protest movement is only going to increase," he said.

Late in 2011, an anti-terrorism court handed down a double death sentence to Qadri for murder and terrorism. The sentence was appealed and upheld by the Supreme Court late last year.

More than 100 people are charged with blasphemy each year in predominantly Muslim Pakistan, many of them Christians and other minorities. No one has yet been hanged, but those convicted languish in prison.

Controversy over the law has exposed the growing gap between religious conservatives and liberals in Pakistan, with hard-line religious leaders considering Taseer a blasphemer himself for even criticising the law.

Some lawyers showered Qadri with rose petals when he first arrived in court days after the killing. The judge who first convicted him was forced to flee the country after death threats.