Nepal earthquake: Before and after

Thousands of people have lost their lives and thousands more have been injured in a 7.8-magnitude earthquake that hit Nepal's capital Kathmandu and its surrounding areas. Mount Everest was also struck by deadly avalanches after the quake on Saturday.

Officials have warned that the number of casualties could rise as rescue teams reach remote mountainous areas of western Nepal.

Many of the country's historic sites have been severely damaged, including temples and monuments.

At least four out of seven Unesco World Heritage sites in the Kathmandu valley - three of them ancient city squares - were badly affected.

KathmanduThe capital's Durbar Square - the royal Nepalese residence until the 19th century - has also suffered, with many buildings reduced to rubble.

Durbar Square, Kathmandu: 13 February 2013

Durbar Square, Kathmandu: 27 April 2015

Durbar Square, Kathmandu: February 2015

Durbar Square, Kathmandu: 27 April 2015

Also in the capital, the 60m (200ft) nine-storey Dharahara tower, built in 1832, collapsed.

Dharahara tower via satellite before and after the quake

Temporary shelters have been set up on open spaces in the city - such as fields and stadiums. They offer some protection to families who have lost their homes or those too scared to stay inside after the quake and powerful aftershocks.

Kathmandu stadium via satellite before and after the quake

BhaktapurIn Bhaktapur, which had been the country's best preserved old city, initial reports claim half of all buildings have been destroyed and 80% of temples damaged.

The ancient city, one of the worst-affected areas, lies to the east of the capital.

Durbar Square, Bhaktapur: October 2014

Durbar Square, Bhaktapur: 27 April 2015

Durbar Square, Bhaktapur: February 2015

Durbar Square, Bhaktapur: April 2015

Search and rescue operationInternational teams of rescuers and medical experts are arriving in Nepal to help hunt and care for earthquake survivors.

INTERACTIVE

• How a search and rescue operation is carried out
  
• Strong buildings×
  Rescue workers need to be swift to assess where they are most likely to find survivors inside collapsed buildings. Stairwells or the spaces under large concrete beams can provide what rescue workers call 'voids', in which people may have survived.
  
  
• Video cameras
  Video cameras placed on the end of flexible poles can be squeezed through gaps in the rubble to help locate survivors. Using this technique means time is saved as less rubble is shifted unnecessarily. Thermal imaging equipment can also be used to locate survivors as their body heat can warm the rubble around them.
  
  
  
• Listening for survivors
  Specialist sound equipment can detect the faintest of noises to within a few metres. Silence on the site is needed while a member of the rescue team bangs three times and hopes to hear a response. Carbon dioxide detectors can be used to find survivors rendered unconscious. They work best in confined spaces where they detect the greater CO2 concentration in the air exhaled by those still breathing.
  
  
• Weak buildings
  Many of the buildings in Nepal collapsed in the initial earthquake or the aftershock. Many older neighbourhoods in the capital, Kathmandu, were made up of poorly-constructed brick buildings and these were largely destroyed in the disaster. Fewer, modern structures collapsed.
  
  
• Local knowledge
  Local people often know the best locations to begin the search for survivors. After speaking to them rescue workers can quickly select the most promising place to begin their work. Many local people have also joined in the search for survivors.
  
  
• Search and rescue
  The co-ordinating agency, usually the UN, and the host country, have to take the difficult decision of when to stop looking for a few remaining trapped people and concentrate resources on looking after the thousands of other survivors. The average time for this switch is between five and seven days, but individuals have been known to survive as long as 13 days, if they have access to water.
  
  
• Rescue dogs
  Dogs are extremely effective at using their sense of smell to pick up on signs of life that human rescuers cannot. They are also able to cover large areas quickly, speeding up the search and rescue process.
  
  
• Lifting equipment
  Diggers and hydraulic jacks are among the heavy machinery that rescue workers employ to shift rubble. Large concrete slabs on the outside of buildings can be pulled aside by diggers, enabling rescuers to get a view of any people still trapped inside. Rescue workers are also taking chainsaws and other power tools to cut through wreckage.
  
  
• Shifting rubble
  Before the heavy-lifting equipment arrives, rescuers use pick axes and shovtels to digs through the rubble. Other tools used by rescuers include chainsaws, disc-cutters and rebar cutters - which can be used to tackle the metal bars in reinforced concrete.
  

The United Nations, which estimates 6.6 million people live in the districts affected by the earthquake, is helping to co-ordinate rescue efforts.

Many have been left homeless by the disaster and the country is already reported to be running out of water and food. There are also frequent power cuts.

The British organisation, Search and Rescue Assistance in Disasters (SARAID) has sent a team of experts with 1.5 tonnes of specialist equipment. This includes an electrical power generator and power tools for cutting through concrete and steel.

They also have their own tents and food supplies, so they will not be a drain on local resources.

India and China are among the other countries to send teams of rescuers.