ISLAMABAD (AFP) - A powerful bomb tore through a busy Shi'ite mosque in southern Pakistan on Friday, killing more than 60 people in the country's deadliest sectarian attack in nearly two years.

The blast hit the mosque in Shikarpur in Sindh province, around 470km north of Karachi, as hundreds of worshippers attended Friday prayers.

Pakistan has suffered a rising tide of sectarian violence in recent years, most of it perpetrated by hardline Sunni Muslim groups against minority Shi'ite Muslims, who make up around one in five of the population.

Sindh health minister Jam Mehtab Daher told AFP that "the death toll from the attack has increased to 61".

"There are 54 dead bodies in Shikarpur hospital. Seven others died in Sukkur and Larkana hospitals," he said.

Shaukat Ali Memon, the medical superintendent of Civil Hospital in Shikarpur, earlier gave a death toll of 48.

Hundreds of people rushed to the scene after the blast to try to dig out survivors trapped under the roof of the mosque, which collapsed in the explosion, witness Zahid Noon said.

Television footage of the aftermath showed chaotic rescue scenes as people piled the wounded into cars, motorbikes and rickshaws to take them for treatment.

"The area is scattered with blood and flesh and it smells of burnt meat, people are screaming at each other... it is chaos," Noon told AFP.

"A huge contingent of police and rangers is present here and ambulances from the nearby towns have started to arrive."

Local resident Mohammad Jehangir told AFP he had "felt the earth move beneath my feet" as he prayed at another mosque around 1.5km away.

An official with a national Shi'ite organisation, Rahat Kazmi, told AFP that up to 400 people were worshipping in the mosque when the blast struck.

RISING TIDE OF VIOLENCE

Sainrakhio Mirani, police chief of the region told AFP officers were still working to determine whether it was a suicide bombing or whether the 6-7kg bomb was detonated remotely.

It is the bloodiest single sectarian attack in Pakistan since March 2013, when a car bomb in a Shi'ite neighbourhood of Karachi killed 45.

A spokesman for the shadowy Jandullah militant group, a splinter faction of the Pakistani Taleban, said they were behind the blast.

"We claim responsibility for attack on Shi'ites in Shikarpur very happily," Ahmed Marwat told AFP.

Friday's attack came as Prime Minister Nawaz Sharif visited Karachi, the capital of Sindh province, to discuss the law and order situation in the city.

Karachi, Pakistan's biggest city and economic heart, has wrestled for several years with a bloody wave of criminal, sectarian and political murders.

Anti-Shi'ite attacks have been increasing in recent years in Karachi and also in the southwestern city of Quetta, the northwestern area of Parachinar and the far northeastern town of Gilgit.

Around 1,000 Shi'ites have been killed in the past two years in Pakistan, with many of the attacks claimed by the hardline Sunni group Lashkar-e-Jhangvi (LeJ).

A report by the US Institute of Peace this week warned that sectarian militant groups were growing in strength in rural areas of Sindh, a province which has escaped much of the worst of the violence that has wracked Pakistan over the last decade.

Pakistan has stepped up its fight against militants in the past month, following a Taleban massacre at a school in the northwestern city of Peshawar.

Heavily armed gunmen went from room to room at the army-run school murdering 150 people, most of them children, in an attack that horrified the world.

Since then, the government has ended a six-year moratorium on executions in terror-related cases and pledged to crack down on all militant groups.