The bomb exploded in a car park next to a mosque where prayers marking the festival were taking place, senior police official Mohammad Hashim told AFP.
Quetta police chief Ahsan Mehboob said a bomb disposal team had concluded that it was a suicide car bomb, as he raised the official toll from 10.
“The death toll is 11 now as one of the wounded men died at the hospital,” Mehboob said.
“Remains of a badly mutilated body were found in the car. It appears that he was not wearing the explosives on his body but he had planted those in the car and detonated when he could not go beyond the parking lot,” Mehboob told AFP.
“Our security was alert, so he could not go beyond the parking, otherwise he might have caused a lot more casualties,” he said, adding that all the dead had been identified by relatives except the suicide bomber.
Quetta police official Hamid Shakil said two women and a seven-year-old boy were among the dead.
Several cars parked nearby caught fire from the blast and one house suffered blast damage, witnesses said.
Live television footage showed swirls of thick black smoke rising from the area as people ran into the street, some pushing their cars to safety, while ambulances carried away the wounded.
Hashim said there had been no immediate claim of responsibility and police could not speculate who might be behind the bombing.