A bomb explosion has ripped through a major hospital where a group of lawyers had gathered in the restive city of Quetta in southwest Pakistan.

Pakistani media reports said at least 70 people were killed and over 110 others injured when the bomb went off in the emergency ward of the hospital on Monday.

Local media had initially put the death toll at over 90, but the figure was later revised down.

Dozens were injured in the incident which took place when a group of lawyers gathered in the hospital to accompany the body of a prominent attorney who had been shot earlier in the day.

Bilal Anwar Kasi, who was the former president of Balochistan Bar Association, was shot dead by unidentified gunmen in the city.

Reports said gunshot were heard as police surrounded the hospital and cordoned off the area after the blast.

Balochistan Home Minister Sarfaraz Bugti blamed the bombing on "a security lapse," saying he was personally investigating it. He said it was too early to determine which group or persons are behind the attack.

Ban: Pakistan bomb attack "particularly appalling"

Reacting to bomb attack on Pakistan’s hospital in Quetta, UN Secretary-General Ban Ki-moon condemned the incident as "terrorist bombing," saying it was "particularly appalling" that the attack targeted a group of mourners, AFP reported.

"The targeting of mourners at a civilian hospital makes the attack particularly appalling," said Ban's spokesman, Farhan Haq.

The UN chief urged the Pakistani government to do its utmost to bring those behind the attack to justice.

Both a pro-Taliban militant group in Pakistan, known as Jamaat-ur-Ahrar, as well as the Daesh terror group have claimed responsibility for the bomb blast at Quetta hospital.

"The Tehreek-e-Taliban Pakistan Jamaat-ur-Ahrar takes responsibility for this attack, and pledges to continue carrying out such attacks. We will release a video report on this soon," the group’s spokesman said hours after the attack in an email, Reuters reported.

The group had already carried out a bomb attack in the eastern Pakistani city of Lahore in March, which left over 70 people, many of them children, dead at a crowded park.

Later in the day, Daesh also said through its Amaq news outlet that one of its members "detonated his explosive belt at a gathering of justice ministry employees and Pakistani policemen in the city of Quetta."

Balochistan has been witnessing ethnic violence and numerous attacks for years, with minority Shia and Hazara community in the province being the regular target of kidnapping and murders by extremist militants.

​The poverty-stricken province, which is rich in gas and mineral resources, shares borders with neighboring Afghanistan to the north and Iran to the east.

The worst attack on Hazara Shias came in early 2013, when more than 180 members of the community were killed in two bombings in Quetta.

Thousands of people have been killed over the past decade as a result of the surge in violence in Pakistan.

Pro-Taliban elements killed over 150 people, most of them children, in an armed assault on a school in the northwestern city of Peshawar in December 2014.