The magnitude-six shaker is one of the largest since the Oct. 8th earthquake that killed nearly 80,000 people.
Aid workers continue to race against time hoping to help hundreds of thousands of homeless survivors before snow moves in. Underscoring the danger, four children were burned Sunday when a tent caught fire.
Doctors are stepping up efforts to inoculate survivors against diseases likely to spread in crowded camps.
Pakistan's foreign ministry says a highly anticipated border opening with India (search) Monday is being held up by procedural glitches. The two countries are trying to ease the flow of aid.
Earthquake victims won't initially be allowed to cross the heavily militarized border dividing Indian and Pakistani Kashmir (search) in this week's much-anticipated opening of the frontier because of procedural glitches, officials on both sides said Sunday.
Pakistani Foreign Ministry spokeswoman Tasnim Aslam told The Associated Press that neither India nor Pakistan had provided the other with lists of people approved to cross as part of an agreement between the South Asian rivals to ease the flow of aid following the quake.
"It doesn't look likely. We have not yet received any list from India and our list has not gone to India," she said, adding that she hoped the paperwork would be exchanged Monday. Each country would then have 10 days to process the names, though they could do it faster.
The announcement was the latest disappointment since India and Pakistan agreed a week ago to open a frontier that has been mostly sealed for nearly six decades.
The accord, originally supposed to open five crossing points, signaled a warming of ties following the quake, and gave hope to residents that they could cross over to check on relatives and visit aid camps being set up on the border.
However, India on Saturday said that just one camp would be ready by Monday, citing logistical difficulties such as landslides and land mines near the crossings.
Two senior officials in India's Jammu-Kashmir state — one civilian and one military — said no civilians would be allowed to cross on Monday and only relief supplies would be delivered across the Punch-Rawalkot crossing. Both spoke on condition of anonymity because of the sensitivity of the matter.
The military official said India's key concern was that Pakistani-based militants might be able to cross into its territory and join a 16-year-old insurgency there against Indian forces. For this reason, the official said, India must be able to closely scrutinize the identities of those crossing.
Ata Ullah, the deputy police chief in the Pakistani Kashmir city of Muzaffarabad, also cited Indian security concerns as a reason for the hold-up.
"We are willing to allow people to go, but India, for security, won't let people" cross, he said.
Sunday's magnitude-6.0 aftershock, one of the biggest since the original 7.6-magnitude quake, unleashed landslides that temporarily blocked traffic near Balakot, said Ali Hassan of the Pakistani agency in charge of road-clearing.
Mohammed Rafeek, a resident of a tent camp on the outskirts of the city, said the tremor frightened many people. "Some people screamed. We all ran outside. No one is taking chances anymore," he said.
India and Pakistan have fought two of their three wars over Kashmir. But cooperation over quake relief appears to be helping heal the rifts.
The quake killed about 80,000 people, most of them on the Pakistani-controlled side of divided Kashmir. It left about 3 million people homeless and hundreds of thousands are still without any form of shelter as the harsh Himalayan winter fast approaches.