Pakistan says more than 1,000 people may have died in a powerful quake that also hit north India and Afghanistan.
The 7.6-magnitude quake with the epicentre 80km (50 miles) north-east of Islamabad wiped out several villages.
At least 500 died in North-West Frontier province in Pakistan. More than 450 lost their lives in the disputed territory of Kashmir.
In Islamabad, people rushed to dig with bare hands to rescue those trapped when an apartment building collapsed.
Pakistani President Pervez Musharraf, who was visiting the site, said the quake was a "test of the nation".
Several countries have offered to send emergency aid.
In a message to Mr Musharraf, Indian Prime Minister Manmohan Singh said: "While parts of India have also suffered from this unexpected natural disaster, we are prepared to extend any assistance with rescue and relief which you may deem appropriate."
The earthquake, which was registered at 0350GMT, was felt as far away as the Afghan capital, Kabul, and India's capital, Delhi. Several aftershocks followed.
Maj Gen Shaukat Sultan, President's Musharraf's spokesman, told the BBC: "I would say it is massive damage that has been caused. I would say that the casualties may not be hundreds - but much more."
Interior Minister Aftab Sherpao told local television: "We have reports that several entire villages have been wiped out."
The head of police in the North West Frontier Province told AFP news agency "between 550 and 600" people had died and the figure was likely to rise.
In Pakistani-controlled Kashmir 250 bodies have been recovered of the more than 2,000 feared dead, an official told the BBC from the provincial capital, Muzaffarabad.
"All official buildings have collapsed," he said.
Landslides have blocked all access roads to Muzaffarabad, where there is no electricity and telephones.
Part of the upmarket Margala Towers residential complex collapsed in Islamabad.
One rescuer, Rehmatullah, said: "I rushed down and for some time you could not see anything because of the dust... We pulled out one man by cutting off his legs."
Karam Usmani, a 28-year-old sub-inspector with Islamabad police told the BBC: "I heard the cries of the people in the debris and with my bare hands I started to dig and I pulled out one dead body.
"But I managed to rescue another man of 35 and carried him on my shoulders to the ambulance."
In Indian-administered Kashmir, 200 are confirmed dead - including 15 soldiers - and 600 injured.
The town of Uri close to the Line of Control that separates divided Kashmir was worst hit, with 104 dead.
The administration is working overtime to restore essential supplies like electricity and water disrupted by the earthquake, says the BBC's Altaf Hussain in Srinagar.
Ben Phillips of Oxfam told the BBC a meeting of relief organisations was under way and is liaising with the UN and the Pakistani government on supplying aid.
Mr Phillips said the initial requirement would be for tents, blankets, food aid and medical supplies.
In other reports around the region:
- A meeting attended by India's prime minister in the northern city of Chandigarh was stopped after his bodyguards ordered an immediate evacuation following the tremors.
- The 200-year-old Moti Mahal fort in Poonch district, Indian-administered Kashmir, has collapsed.
- One child was killed and six injured in a school collapse in Rawalpindi, Pakistan's information minister said.