Reuters/Stringer
A rescuer looks at a damaged house, after a 7.9 magnitude earthquake hit Nepal.
A Nepalese diplomat said there are "possibly hundreds dead" and the government there said at least 114 deaths have been confirmed so far, according to Agence France-Presse.
Meanwhile, the Associated Press reported that Indian officials said there are at least 20 confirmed deaths in their country, which neighbors Nepal.
Kathmandu's decrepit buildings, crisscrossed by narrow alleys, are home to large families. A 1934 quake of magnitude 8.3 in the impoverished Himalayan nation killed over 8,500 people.
At the main hospital in Kathmandu, people with broken limbs and arms were being rushed in for treatment. It was unclear how many people were injured.
A girl died after a statue fell on her in a park in Kathmandu, a witness said, while another died in India when her house collapsed.
An historic tower built in the 19th century in Kathmandu collapsed, trapping at least 50 people, Nepal media reported.
The Dharara Tower, built in 1832, had been open to visitors for the last 10 years and had a viewing balcony on its eighth floor.
One body was removed from the tower and a second lay further up the road, a Reuters witness said.
A Reuters reporter in Kathmandu said he had seen some buildings collapse and walls of several houses reduced to rubble. "Everyone is out in the streets, people are rushing to the hospital," the reporter said.
The city is home to ancient, wooden Hindu temples. Photographs posted online showed buildings left in rubble, large cracks along roads and residents sitting in the street holding babies.
Mountaineer Alex Gavan tweeted from Mount Pumori, about 8 km (5 miles) west of Mount Everest, that the quake had caused an avalanche on Everest:
Everest base camp huge earthquaqe then huge avalanche from pumori.Running for life from my tent. Unhurt. Many many people up the mountain.
- Alex Gavan (@AlexGAVAN) April 25, 2015
Reuters/Stringer TPX
An Indian security personnel stands near a collapsed house after an earthquake in Siliguri, India, April 25, 2015.
"Massive tremors have been felt here in Delhi and several other parts of India," said a newsreader on NDTV in Delhi.
"You can see pictures of our Delhi studios, where the windows rattled and everything shook for a very long time, for a minute perhaps or longer," she said as footage showed studio ceiling camera lights shaking.
A police officer in the control room of neighbouring Indian state of Bihar said the phone lines were jammed with callers from across the heavily populated state. "We don't know about the casualties, we are flooded with calls."
Reuters/Navesh Chitrakar
People take refuge at a school after a 7.7 magnitude earthquake struck in Kathmandu, Nepal, April 25, 2015.
The U.S. Geological Survey said the quake, initially measured at 7.7 but upgraded to 7.9 magnitude, struck 80 km (50 miles) east of Pokhara. It was only 2 km deep.
"We are in the process of finding more information and are working to reach out to those affected, both at home & in Nepal," tweeted Indian Prime Minister Narendra Modi.
Modi convened a high-level meeting with ministers and top officials to assess the situation. There were no preliminary reports of damage anywhere in India, Home Minister Rajnath Singh told the Press Trust of India.
Nepal emerged in 2006 from a civil war between Maoists rebels and the state that left 17,000 dead. Nepal abolished the monarchy in 2008 and the Maoists laid down their arms.
(Reporting by New Delhi and Kathmandu newsrooms; Writing by Michael Perry; Editing by Nick Macfie)