Provincial Disaster Management Authority (PDMA) says the epicenter of the earthquake was Harnai district of the province and had a depth of 15 kilometres.
Tremors were felt in Quetta, Sibbi, Pishin, Muslim Bagh, Ziarat, Qila Abdullah, Sanjavi, Zhob, and Chaman, the PDMA said in its initial report.
The injured, which include women and children, have been shifted to the District Headquarters Hospital in Harnai.
Balochistan Chief Minister Jam Kamal Khan said that assistance and evacuation efforts were under way.
"Blood, ambulances, emergency assistance, [helicopters] and rest all things are placed ... All departments are working on it," he tweeted.
Security forces also reached the district for rescue and relief efforts, the Inter-Services Public Relations (ISPR) said in a statement.
Army doctors and paramedics were assisting the civil administration with necessary medical care, it said, adding that food and medicines were also transported to remote mountainous district Harnai, which was the worst-affected area where a lack of paved roads, electricity and mobile phone coverage hampered rescue efforts.
Nine critically injured patients were airlifted to Quetta in Pakistan Army helicopters, according to the statement.
In 2005, a 7.6 Richter-scale quake had killed more than 90,000 people and dislocated over 3.5 million, primarily in Pakistani Kashmir and Hazara Division of northwestern Khyber Pakhtunkhwa Province.
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