7.8 magnitude quake slams Nepal; hundreds dead, authorities say

(CNN)A 7.8 magnitude earthquake centered less than 50 miles from Kathmandu rocked Nepal with devastating force early Saturday, killing at least 806 people -- and probably more -- in Nepal's capital city, authorities said.

Afterwards, historic buildings in Kathmandu lay in rubble. The injured wound up being treated outside hospitals in chaotic scenes. Residents, terrorized by a seemingly endless series of aftershocks, huddled outdoors for safety.

The death toll was reported by Nepal's Ministry of Home Affairs. But given that the rescue effort is still in its early stages and that people in outlying areas may well have been affected, as well, it seems probable the number will rise.

And Kathmandu, which sits in a valley surrounded by the Himalayas, has a population of 1 million people.

Aid agencies expressed concern for the welfare of survivors in the coming days, as overnight temperatures are expected to drop and people will need to make do without electricity, running water and shelter.

The international community must react quickly to save lives -- particularly those of children -- said Devendra Tak, of the aid agency Save the Children.

\"With every minute the situation becomes worse,\" he said. \"Tonight is going to be a very tough night out there for people in Kathmandu and for people in the surrounding villages.\"

Food, clothing and medicine will be urgently required, he said.

Those who will be spending the night outside have already endured a day that has been difficult beyond belief. People who experienced the quake spoke by telephone with CNN, describing scenes of chaos, fear and suffering.

CNN's Manesh Shrestha said he saw five bodies at a hospital to which he walked to seek treatment for his own injuries. People with severe injuries were lying outside, with doctors administering CPR to at least one of them, Shrestha said.

\"It's quite chaotic,\" he said by phone. \"People are wailing, crying.\"

Shrestha, who had been cut and was in need of stitches, was turned away because other people had more dire need of care. He saw people lying outside with broken bones and head injuries.

Not far away avalanches triggered by the quake thundered down Mount Everest, sending mountaineers running for cover.

\"Everest base camp huge earthquake then huge avalanche from pumori,\" Twitter user Alex Gavan said. \"Running for life from my tent. Unhurt. Many many people up the mountain.\"

The quake, which struck at 11:41 a.m. local time (1:56 a.m. ET), occurred at a depth of 9.3 miles, which is considered shallow and more damaging than a deeper quake. It was reported by people in the area as having lasted a long time. On person said he felt as if he were on a ship in rough seas.

The U.S. Geological Survey had at first rated the temblor at 7.5 magnitude but later upgraded the strength. It reported aftershocks of 6.6 and 5.1 magnitude, among many others others. The USGS said, at least 15 aftershocks of magnitude 4.5 or greater had been felt in Nepal so far.

One witness told CNN by phone that people had gathered outdoors in fear. Another said via Facebook that people were listening for news on their car radios.

\"We are scared and waiting for the tremors to end,\" Shiwani Neupane said on Facebook chat from Kathmandu. \"We are all sitting outside because there is more news of another quake.

\"There is no power and families are listening to the FM radio inside their cars,\" Neupane said. \"News of multiple building collapses. I've seen many cracked walls and roads and buildings. The Dharara was packed with people a while ago. There are police everywhere trying to move rubble to make space on the roads for ambulances. Everyone is very scared.\"

People experienced quake as 'severe' to 'violent'

The force of the quake was said by people who contacted the USGS to be from \"severe\" to \"violent,\" nearly the highest rating on the intensity scale. Tremors were felt as far as New Delhi, more than 200 miles away in neighboring India. An official said they were felt there at magnitude 5.0.

The shaking was rated as \"strong\" to \"severe\" on the USGS ShakeMap. CNN sister network CNN-IBN reported that roads in the area were out.

Kanak Masni, a journalist in Kathmandu, told CNN by phone that a historic building in Kathmandu called the Dharahara -- also known as the Bhimsen Tower -- had tumbled down. The building, built in 1832, was nearly 63 meters (207 feet) tall and provided visitors with a panoramic view of of the Kathmandu valley.

Masni told CNN by telephone that this appeared to be \"the most massive earthquake to hit central Nepal since 1934.\" In that quake, which was 8.0 magnitude and centered near Mount Everest, more than 10,000 people were reported killed.

IBN reporter K. Dhiksit looked out his window in Kathmandu and saw the collapsed walls of many buildings. As he watched, an aftershock rattled the street. He heard \"big booming sounds,\" he said, and saw people fleeing into the streets.

Photos of caved-in and toppled buildings appeared on social media.

India's Prime Minister Narendra Modi said in a tweet, \"We are in the process of finding more information and are working to reach out to those affected, both at home & in Nepal.\"