Balochistan Home Minister Safraz Bugti said 103 people were also injured by the suicide bombing in the state capital, Quetta.
The explosion hit moments after a group of lawyers brought in the body of colleague Bilal Kasi, the president of the Balochistan Bar Association, after he was shot dead by unknown assailants in Quetta earlier in the morning.
Most of the dead and injured were lawyers, Anwar ul-Haq, a spokesperson for Balochistan state government, told reporters.
Irfan Saeed, an eyewitness, told Anadolu Agency the blast occurred in the midst of a crowd gathered outside the hospital's emergency ward. He said several bodies were lying on the hospital floor as staff ran for safety after the blast.
Prime Minister Nawaz Sharif called the blast "cowardly" and pledged his government and security forces will continue their attempts to defeat militants based in the country.
The UN condemned the attack and in a statement said the “targeting of mourners at a civilian hospital makes the attack particularly appalling”.
In Washington, the White House also condemned the attack "in the strongest terms.
"That this attack occurred at a hospital and appeared to target a gathering of lawyers mourning the death of a respected colleague makes it all the more heinous," spokesman Josh Earnest said in a statement.
The local government declared a state of emergency and prepared to transfer the injured to private hospitals.
No group has claimed responsibility though similar attacks have frequently been claimed by the Taliban.