The U.S. Geological Survey said the quake had a magnitude of 7.7 on the Richter scale. The agency said the earthquake was likely to cause large casualties since it was strong enough to damage most or all buildings near the epicenter.
Jan Muhammad Buledi, a spokesman for the provincial government, said at least 55 deaths had been confirmed, the newspaper Dawn reported. The quake was centered in the sparsely populated Awaran region.
A spokesman for the national disaster management agency said most of the deaths occurred when buildings collapsed.
A medical team traveling to Awaran was attacked by gunmen en route, officials said.
Balochistan is a large province bounded on the west by Afghanistan and Iran and on the southwest by the Arabian Sea.
A small island 30 to 40 feet high rose in the sea just off Gwador after the quake, Dawn reported. Officials said hundreds of people came to the coast to see it.
Minor tremors were felt as far away as New Delhi, while office workers in the Indian city of Ahmedabad, near the Pakistan border, fled from buildings into the street, witnesses said.