At least 80 people have been killed so far in the quake that struck Awaran district in Balochistan province, according to a spokesperson of Frontier Corps, Balochistan.
About 80 injured people, including women and children, were brought to the Civil Hospital in Khuzdar, a spokesman for the Balochistan government said.
Reports of deaths had been received from Awaran and Turbat districts, he said. Hundreds of mud-brick houses collapsed or were damaged in Awaran and Khuzdar areas, officials said.
Six bodies were found in Awaran bazar and four more in far flung villages of the district, said Deputy Commissioner Abdul Rasheed Baloch.
"I fear more people are trapped inside collapsed houses," he said.
Ghulam Baloch, an administration official from Khuzdar, said, "Houses and shops have collapsed and the casualties could increase."
Houses were also damaged in Pasni and Windar but details were awaited from these areas, Baloch said.
The army despatched 300 soldiers, rescue and medical teams and a helicopter to the worst-hit areas. Chief Minister Abdul Malik said an emergency had been declared in Awaran, seven to eight hours' drive from Quetta, the provincial capital.
The quake struck at 4.29 pm Pakistani time at a depth of 23 kilometres.
Tremors were felt in Karachi, Hyderabad, Larkana and other towns and cities of Sindh province.
Reports said the quake was also felt in Lahore, Rawalpindi and Islamabad.
The tremor was also recorded in Srinagar and Delhi.
The tremors that lasted almost a minute caused widespread panic in many places.
People rushed out of their offices and homes in Karachi, the country's largest city, and other parts of Sindh and Balochistan provinces.
National Seismic Monitoring Centre Director Zahid Rafi told PTI that the tremors were of "great intensity" in Quetta and in some remote areas of Balochistan.
"The affected areas include Jaffarabad, Noskhi, Kalat, Windar, Naseerabad, Phunjgur and Mastung," he said.
"The shockwaves were strong enough to even be felt in Karachi, Hyderabad, Thatta, Khairpur and Larkana," Rafi said.