The blast that hit the the Civil Hospital followed the killing of President Balochistan Bar Association Bilal Anwar Kasi, who was shot dead by unidentified gunmen in Quetta earlier in the day, Dawn online reported.
The explosion took place soon after lawyers arrived at the hospital when the Kasi's body was brought in, police said.
Several lawyers were reported injured in the explosion and aerial firing could still be heard at the premises.
TV reports showed people trying to exit the hospital. Journalists present at the premises also came in the line of fire, Dawn online added.