A massive 7.8 magnitude earthquake killed hundreds of people Saturday as it ripped through large parts of Nepal, toppling office blocks and towers in Kathmandu and triggering an avalanche that hit Everest base camp.

Officials said at least 449 people are known to have died in Nepal but that the toll could be much higher, while more than two dozen people were also reported killed in neighbouring India, China and Bangladesh.

"The death toll based on information received on our network across the country has reached 449," Nepal's national police spokesman Kamal Singh Bam told AFP.

"Deaths have been reported from all regions except the far west. All our security personnel have been deployed to rescue and assist those in need."

Officials said an avalanche had buried parts of Mount Everest's base camp in Nepal where hundreds of mountaineers have gathered at the start of the annual climbing season.

"An avalanche from Mt. Pumori has hit the base camp, burying a part of it," Gyanendra Kumar Shrestha, an official in Nepal's tourism department, told AFP.

"We are trying to assess how many are injured. There might be over 1,000 people there right now, including foreign climbers and Nepalese supporting staff."

AFP Nepal bureau chief Ammu Kannampilly, on an assignment to Everest, was among those caught up in the chaos and reported that snowfall meant it was impossible for helicopters to reach the area.

Two experienced mountaineers said that panic erupted at base camp which was full of climbing teams and had been "severely damaged", while one said the quake triggered a "huge avalanche".

-- Historic tower collapses --

But the worst damage was reported in Kathmandu, where the historic nine-storey Dharahara tower, a major tourist attraction, was among the buildings to have been brought down.

At least a dozen bodies were taken away from the ruins of the 19th century tower, according to an AFP photographer who saw similar scenes of multiple casualties in other parts of the city.

While contact with Nepal was sporadic, a senior Nepalese diplomat warned that the final toll could run into many hundreds.

"We have received reports that there is a big loss of property and life in Nepal," Krishna Prasad Dhakal, the deputy chief of mission at Nepal's Embassy in New Delhi, told AFP.

"Possibly hundreds of people have died in various parts of the country, particularly in Kathmandu and Pokhara."

At least 26 people were known to have died in India, including 17 in the eastern state of Bihar, while buildings in the capital New Delhi had to be evacuated.

The United States Geological Survey and India's meteorological service said the shallow quake struck 77 kilometres (48 miles) northwest of Kathmandu at 0611 GMT, with walls crumbling and families racing outside their homes.

"The walls of houses have collapsed around me onto the road. All the families are outside in their yards huddled together," an AFP reporter said in Kathmandu.

Another resident recounted scenes of panic and mayhem.

"Everything started shaking. Everything fell down. The walls around the main road have collapsed. The national stadium's gates have collapsed," Anupa Shrestha said.

The quake tore through the middle of highways in the capital and also caused damage to the country's only international airport which was briefly closed.

Kari Cuelenaere, an official at the Dutch embassy, said the impact had swept the water out of a swimming pool at a Kathmandu hotel where Dutch national day was being celebrated.

"It was horrible, all of a sudden all the water came up out of the pool and drenched everyone, the children started screaming," Cuelenaere told AFP. "Some parts of the city fell down, there was dust rising... There were many (rescue) helicopters.

Aftershock tremors could be felt more than two hours after the initial quake.

Initially measured at 7.5 magnitude, the quake was later adjusted to 7.8, with a depth of 15 kilometres, the USGS said. It hit 73 kilometres east of the tourist town of Pokhara.

- Tremors felt across region -

Witnesses and media reports said the tremors lasted between 30 seconds and two minutes.

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

The AFP office in Delhi was evacuated twice following the quake.

China's official Xinhua news agency said that two people, including an 83-year-old woman, were killed in the Tibet region as a result of the quake.

The earthquake was also felt across large areas of Bangladesh, triggering panic in the capital Dhaka as people rushed out onto the streets.

In the garment manufacturing hub of Savar, on the outskirts of Dhaka, at least 50 workers were injured after the quake set off a stampede in a garment factory, according to the private Jamuna television.

The area has a history of earthquakes, with a 6.8 magnitude quake that hit eastern Nepal in August 1988 killing 721 people.

A magnitude 8.1 quake killed 10,700 people in Nepal and eastern India in 1934.

Deadliest earthquakes of the past 30 years
Kathmandu (AFP) April 25, 2015 - Hundreds are feared dead after a powerful 7.9 magnitude quake rocked Nepal on Saturday. Below is a list of some of the world's deadliest earthquakes in the past 30 years.

-- August 11, 2012: Twin earthquakes with a magnitude 6.3 and 6.4 leave 306 dead and more than 3,000 injured near the Iranian city of Tabriz.

-- March 11, 2011: Nearly 18,900 are killed when a tsunami triggered by a massive magnitude 9.0 undersea quake slams into the northeast coast of Japan, triggering a nuclear crisis at the Fukushima Daiichi atomic plant.

-- October 23, 2011: An earthquake of 7.2 magnitude rocks eastern Turkey, leaving more than 600 dead and at least 4,150 injured.

-- January 12, 2010: Magnitude 7.0 quake hits Haiti, leaving between 250,000 and 300,000 dead.

-- April 14, 2010: A 6.9-magnitude quake hits Yushu county in northwest China's Qinghai province leaving 3,000 people dead and missing.

-- May 12, 2008: A quake measuring 8.0 hits China's southwest province of Sichuan, leaving more than 87,000 people dead or missing.

-- May 27, 2006: A powerful quake in Indonesia's Yogyakarta region kills 6,000 and leaves 1.5 million homeless.

-- October 8, 2005: An earthquake of 7.6 kills more than 75,000 people, the vast majority of them in Pakistan's North West Frontier Province and the Pakistani-administered zone of Kashmir state. Some 3.5 million are displaced.

-- March 28, 2005: An earthquake on Indonesia's Nias island off Sumatra leaves 900 dead.

-- December 26, 2004: A massive undersea earthquake off the coast of Sumatra island triggers a tsunami which kills 220,000 in countries around the Indian Ocean, including 168,000 in Indonesia.

-- December 26, 2003: A quake measuring 6.7 hits the Iranian city of Bam, killing at least 31,884 people and injuring 18,000.

-- January 26, 2001: A massive 7.7 earthquake hits the western Indian state of Gujarat, killing 25,000 people and injuring 166,000.

-- September 30, 1993: A 6.3-magnitude quake hits the western Indian state of Maharashtra, killing 7,601.

-- October 20, 1991: A quake measuring 6.6 hits the Himalayan foothills of Uttar Pradesh state in India, killing 768.

-- August 20, 1988: A magnitude 6.8 quake hits eastern Nepal, killing 721 people in Nepal and at least 277 in the neighbouring Indian state of Bihar.

- July 28, 1976: A magnitude 7.8 quake hits Tangshan, in north China's Hebei province. Officials said 242,000 people died, although some western sources said the toll was higher.

-- January 15, 1934: Magnitude 8.1 quake hits eastern Nepal and Bihar state in neighbouring India killing 10,700 people.