Pakistan's army called Saturday's devastation "a national tragedy".
In the capitals of Pakistan, India and Afghanistan, buildings shook and walls swayed for about a minute, and panicked people ran from their homes and offices.
Tremors continued for hours afterward. Communications throughout the region were cut.
About 1000 people died in Pakistani Kashmir, said Sardar Mohammed Anwar, the top government official in the area.
"This is my conservative guess, and the death toll could be much higher," Anwar told Pakistan's Aaj television station. He said most homes in Muzaffarabad, the area's capital, were damaged, and schools and hospitals collapsed.
At least 550 people died in Pakistan's North West Frontier Province, the local police chief said.
Troops have been deployed to
the stricken areas
"The death toll is between 550 and 600 in North West Frontier Province and it is likely to rise," Riffat Pasha, the provincial head of police told AFP.
Another police official said more than 500 people had died in the province's remote districts of Mansehra and Malakand.
"We still do not have any full death count but the reports sent by different police stations say between 500 to 600 people have died," Mansehra police official Mohammad Asghar told AFP.
The quake, which occurred directly on the dividing line between the Indian and Pakistani controlled zones of Kashmir, triggered landslides and sent terrified residents fleeing into the streets.
Senior Pakistani officials described scenes of "massive devastation".
Apartment buildings collapsed
in the earthquake
Thirty-five people were feared killed when a courtroom and two schools collapsed in northern Pakistan during the huge quake, police and officials said.
The Pakistani military said that at least one village in Kashmir had been destroyed and that troops and helicopters had been scrambled to reach the stricken areas.
"There are reports of buildings collapsing in several cities in central Pakistan. We have no exact estimates, but the casualties could be very high," said one Pakistani official, asking to remain anonymous.
The Indian army said at least 31 people - 16 civilians and 15 soldiers - had been killed in the Indian-controlled zone of Kashmir and about 300 taken to hospital.
Indian army spokesman P Sehgal said many soldiers had died when their positions caved in along the line of control, the heavily-militarised de facto border which divides Kashmir into Indian- and Pakistani-administered zones.
Sehgal said others were hit by falling trees and landslides.
The US Geological Survey and the Pakistan Meteorological Department said the quake measured 7.6 on the Richter scale, while the Japanese Meteorological Agency put the temblor higher at 7.8.
The epicentre was around 100km northeast of Islamabad, according to most agencies, although the Earth Sciences Observatory in the French city of Strasbourg said the epicentre was just inside Indian Kashmir.
The quake's epicentre was 100km
northeast of Islamabad
The divided territory of Kashmir is claimed in full by India and Pakistan. Thousands of troops face off on each side of the line of control and the two countries have fought two wars over the territory.
The quake shook the desert town of Quetta, 700km southwest of Islamabad as well as the northern Afghan city of Kunduz, 500km north of the Pakistani capital.
In Islamabad, part of an 11-storey apartment block collapsed leaving dozens of people trapped and neighbours clawing at the rubble in an attempt to free them.
Bloodstained people could be seen trapped beneath huge stone slabs at the scene while desperate cries for help could be heard.
A school in the nearby city of Rawalpindi also came down, killing one child and injuring six others, while Afghan officials said at least two children had been killed near the town of Jalalabad.
Witnesses in Islamabad said the ground shook for more than 30 seconds, rocking buildings and causing widespread panic. A second, less severe jolt lasted about five seconds.
Many mosques in Islamabad started reciting special prayers straight afterwards.
The quake was felt strongly in Indian Kashmir, causing panic and bringing people pouring out onto the streets of the summer capital, Srinagar.
"This is the strongest earthquake I have ever witnessed in my life," said Aisha Begum, 84.
"This is the strongest earthquake I have ever witnessed in my life"
Aisha Begum, 84,
witness to the quake
Screams were heard from across Srinagar as people fled homes, shops and offices fearing they would be buried under rubble.
Doctors at Srinagar's main hospital said more than 200 people were admitted with injuries and shock, while more than 100 people were being treated at an army hospital in the northern town of Uri alone.
The tremor also brought down part of the state-owned television's main transmitter tower on a hill overlooking Srinagar.
The disputed Kashmir region is an area of high seismic activity that lies in the collision zone of the Eurasian and Indian tectonic plates.