Officials said so far, at least 42 people had been killed and 1,117 injured in the new quake in Nepal, which the USGS initially reported as magnitude 7.1, before later upgrading it to magnitude 7.3.
In addition, the national disaster management authority in India said 17 died there. 
The quake, which struck 18km southeast of Kodari, near the base camp for Mt Everest, was measured at a shallow depth of about 18km. A series of aftershocks - including one 6.3 magnitude tremor - later hit in the same area, the USGS reported.
At least 19 buildings have collapsed, officials said, including 10 in Kathmandu.
Police issued a public warning, calling for people to stay in open areas and to send text messages instead of making calls, to prevent the network from becoming jammed.
Al Jazeera's Annette Ekin, reporting from Kathmandu, said that there was "utter panic" in the capital following the quake.
"The earth just started rolling. Everyone ran out onto the streets and all of the shops are now shuttered," she said, adding that the quake seemed to last about 30 seconds.
A woman who works for a finance company in Thamel, in Kathmandu, told Al Jazeera that she had clung to a pillar inside her building when the quake struck.
"I was screaming. It felt like the house was falling," she said.
Al Jazeera's Andrew Simmons, also reporting from Kathmandu, said the quake was so powerful that it made the building he was in "feel like jelly".
Tremors were felt in northern parts of neighbouring India, Afghanistan and Indonesia.
Two hours after the quake struck, our correspondent Ekin said that no one in Kathmandu appeared willing to go back indoors.
"Everyone is outside in the streets. At my hotel, all of the staff and guests are sitting around outside, waiting for more information," she said.
Ekin later went to Kathmandu's Nayabazar district, where a four-storey building had collapsed.
While there were unconfirmed reports of people trapped under the rubble, she said authorities outside the building said no one had been killed.
Kathmandu's airport has been closed, following the quake.
A 7.8-magnitude earthquake struck on April 25, killing at least 8,046 people and injuring more than 17,800.
nepal earthquake kathmandu
Source: Al Jazeera