Local authorities said they had heard some reports of houses that survived the first quake collapsing from the second.
Chief Pakistani meteorologist Arif Mahmood told Pakistani television that Saturday's earthquake was an aftershock and such tremors could continue for weeks.
Pakistan television showed people at the main hospital in Awaran district fleeing into the street. In the provincial capital of Quetta, the tremor was so strong it prompted members of the local parliament to evacuate the building.
Baluchistan is Pakistan's largest but least populated province. The rough terrain and the lack of decent roads have made access difficult for rescue staff. The Pakistani Air Force has been air dropping supplies and using helicopters to ferry injured people for medical care.
But at least two of those helicopters have come under fire from separatist fighters, say Pakistani officials. The Pakistani military has been trying to suppress an uprising in the vast, arid province for years by rebels who want an independent state for the Baluch people.
To the north, Pakistan is dealing with militants who want to overthrow the central government and establish a hard-line Islamic state.
Newly-elected Prime Minister Nawaz Sharif has vowed to pursue peace talks with the militants as a way to end the fighting. But the militants have given little indication they are interested in negotiations. They initially rejected talks with the government and later demanded Islamabad release prisoners and begin withdrawing troops from the group's tribal sanctuary before talks could begin. Recent attacks have also called into question their interest in negotiating.
On Saturday, a spokesman for the Tehreek-e-Taliban criticized Sharif, saying his new government is not serious about holding peace talks. The spokesman, Shahidullah Shahid, did not explicitly reject the offer but his words gave little room for negotiations.
The comments appeared to have been sparked by an interview Sharif made with the Wall Street Journal during a trip to New York, in which he said militants must lay down their arms and follow the constitution. Previously Sharif had not given preconditions for the talks.
"By telling us that we will have to lay down arms and respect the constitution, the prime minister, Nawaz Sharif, showed that he is following the policy of America and its allies," the spokesman said. "We will hold talks with (the government) only when it gets the real power to take decisions."
- AP