ISLAMABAD, Pakistan (CNN) -- More than 18,300 people are estimated to have died in Pakistan, India and Afghanistan as a result of Saturday's magnitude 7.6 earthquake, authorities say. Those numbers are expected to rise once remote areas of Pakistani-controlled Kashmir and the country's North-West Province are reached. Communication to many of those areas was cut off because of the quake, and landslides have rendered roads inaccessible.CNN has confirmed 14,800 deaths in Pakistan, most in Pakistani-controlled Kashmir. The dead include 230 Pakistani soldiers and 250 school girls whose bodies were recovered from a school at Gari Habi Ullaha between Manshera and Muzaffarabad.Pakistani President Gen. Pervez Musharraf issued a plea on Sunday for foreign aid -- specifically, cargo helicopters and relief goods such as tents and blankets. Helicopters are necessary, he said, because roads leading into some remote areas have been buried by landslides and the areas cannot be reached.The Pakistani government has declared three days of national mourning for earthquake victims, to begin Sunday and last until Tuesday. Flags will fly at half-mast for that period, according to a government statement. Musharraf said it was difficult to reach remote areas, "which are mountains anywhere over 10,000 feet.""We can only go by roads, and roads also don't reach to every corner, so therefore it's only helicopter access that we have. Things are not as simple as one would see in the West."He asked the international community to "bear with us. We have formulated our strategy now. UK and U.S., yes, indeed, we will expect helicopter support from you."Musharraf said he had asked the U.S. government to send helicopters from Afghanistan, and had been promised those helicopters although they had not yet arrived.The president planned to tour quake-struck areas again Sunday.Pakistan's military spokesman, Maj. Gen. Shaukat Sultan, told CNN that the country had launched its largest relief operation."In certain areas, the entire villages -- they have collapsed. In certain areas, almost entire towns, they have vanished from the scene," he said.Sultan estimated at least 18,000 people have died in Pakistan alone, and 41,000 are injured. Eyewitnesses report the city of Balakot, in the North-West Province, is destroyed. "It is likely the ground zero," Sultan told CNN. Another military spokesman, Brig. Shah Jahan, said relief and rescue workers have yet to access 30 to 40 percent of the affected areas.Muzaffarabad, the capital of Pakistani-controlled Kashmir, also suffered heavy damage, including a Pakistani army hospital, and had a high casualty toll."It's reasonable to assume the casualties in Balakot alone would be in the few thousand," said CNN Senior International Correspondent Satinder Bindra, who took an aerial tour of the area with the Pakistani army.In Muzaffarabad, mass burials could be seen taking place, he said.An emergency meeting of the Pakistani Cabinet, called by Prime Minister Shaukat Aziz, was taking place Sunday, where officials planned to gather data from various regions.The military's focus is evacuating injured people, establishing forward bases and opening up communications, Sultan said. Bad weather initially hampered effort, but the heavy rain stopped and conditions improved Sunday.More than 24 hours after the earthquake, rescue workers were trying to free some 100 people believed trapped in the rubble of the collapsed Islamabad apartment building. Rescue workers reported hearing voices from under the debris. An estimated 97 people in the building survived; 20 bodies have been found.About 75 families lived in the building, according to Dr. Syed Fazal Hadi, executive director of the Pakistan Institute of Medical Sciences.The total death toll stood Sunday at 18,376, including one death in Afghanistan -- a young girl in Jalalabad who died when a wall of her home collapsed.The quake hit Saturday at 8:50 a.m. (11:50 p.m. ET Friday). Its epicenter was about 60 miles north-northeast of Pakistan's capital, Islamabad. It was felt in major cities, including Islamabad and Lahore, and India's capital of New Delhi. (See scenes of major damage in the capital - :44)Pakistan needs transport helicopters able to carry large machinery that can be used to clear debris. Until roads are cleared, relief operations will have to rely on helicopter flights, Sultan said. Salim Bokhari, group editor with the English-language newspaper "The News," said from Lahore, Pakistan, that he had reports that 250 students were killed when a school building collapsed 40 miles from Islamabad. Also, he said, three school buildings were reported to have been destroyed in the Pakistani-ruled part of disputed Kashmir, killing more than 200 children.In addition, Bokhari said one of three hospitals in Pakistani Kashmir reportedly collapsed.In Amritsar, east of Lahore, a man sobbed as he described losing his business."The earthquake struck and minutes after I got a call that smoke was coming out of my shop. I rushed and saw that my shop was on fire. I have suffered massive losses."Only one death was reported in Afghanistan. A young girl died in Jalalabad when a wall collapsed in her home. A U.S. soldier told CNN the quake was felt in Kabul, but "effects were minimal."Frantic efforts to rescue survivors continued in Islamabad early Sunday morning. Video footage from Pakistani television showed crowds of people climbing on the rubble of an apartment building and attempting to free those trapped under large concrete slabs. Some of the injured were carried away on stretchers. (Watch the latest rescue efforts - 1:10)Many people were still in their beds when the quake struck. Witness Malik Abdul Manan, who lives in Islamabad, said he and his family "woke up and ran out. The shocks went on for a long time." (More witness accounts)Stunned Pakistanis, many covered with blood, were camped out in the streets on Sunday, fearful of returning home because of aftershocks, one of which measured 6.3 in magnitude."Even today, people are scared," Bokhari said.Help offeredPolitical tensions between India and Pakistan over the Kashmir region took a back seat as Indian Prime Minister Manmohan Singh called Musharraf and offered help. Musharraf thanked him for his offer.The two nations have fought three wars -- two of them over Kashmir -- since independence from British rule in 1947.Aziz, who saw aerial views of the devastation, said "we have provided for a lot of alternate housing. Luckily, the weather is not that cold yet so people are living in tents, sleeping bags. Blankets, water, food and a lot of help is coming from all over the country and overseas also."In Indian-controlled Kashmir, or Jammu-Kashmir, the death toll stood at about 256, including 36 Indian soldiers, according to local government, army and police officials.Some 700 other people were injured in Jammu-Kashmir as well, including 82 soldiers, according to the police and military. Local officials estimate more than 1,000 dwellings have been damaged or destroyed across Jammu-Kashmir.Qamar Uz Zaman, director-general of the Pakistani Meteorological Department, told CNN that "this was the strongest earthquake in the area during the last hundred years."The United States, Britain, Germany, Turkey, Japan, the United Nations and non-governmental humanitarian groups have marshaled resources to help the region. (Details)Musharraf and Aziz reviewed rescue and relief operations at the collapsed apartment building -- the 10-story residential Margalla Tower.How the quake compares with othersThe quake was "quite shallow," said David Applegate, senior science advisor for earthquake and geologic hazards for the U.S. Geological Survey. "That means the shaking is going to be very intense."The fact that Islamabad was near the epicenter "means a fairly large urban population has experienced some strong shaking," Applegate said.The National Earthquake Information Center put the quake at 7.6 magnitude, which it considers "major." The Pakistani Meteorological Department put the magnitude at 7.5, and Japan's Meteorological Agency put it at 7.8.In February 2004, a pair of earthquakes registering 5.5 and 5.4 magnitude killed at least 21 people and injured dozens more. Hundreds of homes built of mud, stone and timber were destroyed in a rugged, mountainous area about 90 miles northwest of Islamabad.In January 2001, some 20,000 people died in a magnitude 7.7 quake that was centered in southern India but also caused damage and deaths in Pakistan.CNN Senior International Correspondents Satinder Bindra and Matthew Chance, correspondent Ram Ramgopal, producers Syed Mohsin Naqvi and John Raedler and journalists Mukhtar Ahmed in Srinagar and Tom Coghlan in Kabul contributed to this report.