"This is three hours old and more [deaths] are expected," the Pakistani province of Khyber Pakhtunkhwa's Chief Minister Pervez Khattak told state TV. At least 30 deaths were confirmed there.
The victims included around 12 girls who died while trying to flee their school, an Afghan official told NBC News. Some were crushed in a stampede. Seven more deaths were reported in the city of Jalalabad.
The temblor struck at around 2:10 p.m. (5:10 a.m. ET) and occurred in remote area of the Hindu Kush region of Afghanistan around 28 miles south-southwest of Jarm, according to the USGS. The agency later revised its magnitude from a preliminary 7.7 to 7.5.
The quake came just days after rain fell in many parts of Afghanistan, potentially making mud-built dwellings vulnerable.
The governor of the Afghan province of Badakhshan, where its epicenter was located, told NBC News that "homes were destroyed." Shah Waliullah Adeeb added that authorities had been unable to make contact with some remote districts.
Afghanistan's Chief Executive Abdullah Abdullah said the country's disaster management authority was still trying to gauge the damage.
In the Afghan capital of Kabul, cars stopped in the streets and screaming residents streamed out of homes, offices and schools. Widespread power outages and telephone cuts were reported.
Similar scenes were reported in cities including Islamabad, Lahore and Peshawar in neighboring Pakistan, where the government declared emergency in some areas. The country's army put all non-combat units on standby.
"I just felt it go up and down as if I was on a New York subway on a really rough ride," said NBC News producer Wajahat S. Khan, who was in a hotel in Lahore at the time of the quake. "Everything was moving up and down. My lunch on the table was literally just popping up and down."
Khan added: "The scenes downstairs were really, really chaotic. The panic continued and lasted for a good four or five minutes after the quake."
NBC News producer Mushtaq Yusufzai was eating with his family in Peshawar when the earthquake struck.
"There was no was way to go downstairs so we immediately climbed to the rooftop," he said. "It seemed the entire building was going to collapse. Women and children were crying and traffic was stopped on roads."
At least 55 people were injured in Peshawar, officials said. Some were listed in critical condition.
The country's Supreme Court in Islamabad was in a televised session and judges, lawyers and complainants were shown running out of the room.
The quake was also felt in Indian cities including Srinagar, which is located almost 300 miles away.
Devastating earthquakes are relatively common in the mountainous and seismically-active region. A 7.6-magnitude quake killed around 75,000 people when it hit northern Pakistan on Oct. 8, 2005.