Thousands of people have been killed after a massive earthquake struck Turkey and Syria on Monday.
A search and rescue operation is under way, with specialist teams arriving from around the world.
However, people in some badly-hit areas say rescue efforts have been slow. Some have had to dig with their bare hands to find relatives.
How do you start a search and rescue operation?
When rescuers first arrive at the scene of an earthquake, they assess which collapsed buildings are most likely to contain trapped people.
They do this by looking for "voids" - spaces under large concrete beams or stairwells where survivors can be found.
The possibility a building could collapse further also needs to be taken into consideration, as do other dangers such as gas leaks, flooding and hazardous items, like asbestos in roofs.
While rescuers attempt to reach survivors, support workers watch for building movements and listen out for strange sounds.
Buildings that have completely collapsed are usually the last to be searched, because the likelihood of finding survivors is very slim.
The work of rescue teams is co-ordinated by an agency, usually the United Nations (UN) and the host country. Rescuers are specially trained and work in pairs or bigger teams, while local people are often involved as well.
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What rescue equipment is needed?
To shift rubble, rescue teams use heavy machinery - including diggers and hydraulic jacks.
Large concrete slabs on the outside of buildings can be pulled aside by diggers, enabling rescuers to get a view of any people trapped inside.
Video equipment on the end of flexible poles can be passed through gaps to help locate 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 who are unconscious. They work best in confined spaces where they detect the greater CO2 concentration in the air exhaled by those still breathing.
Thermal imaging equipment can be used to locate people not directly in a rescuer's line of sight, because their body heat can warm the rubble around them.
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What do the rescue dogs do?
Using their sense of smell, specially trained dogs can pick up on signs of life where human rescuers cannot.
Dogs also able to cover large areas quickly, speeding up the search and rescue process.
Do people need to use their bare hands?
Once the large slabs and structures are removed, rescue teams use their hands and small tools like hammers, pickaxes and shovels, as well as chainsaws, disc-cutters and rebar cutters - which can be used to tackle the metal bars in reinforced concrete.
They have protective equipment, including helmets and gloves to protect their hands as they remove sharp pieces of rubble.
However, in some areas of Turkey - where rescue efforts have been slow - local people have been digging through frozen wet rubble with their bare hands.
Bedia Gucum, a restaurant owner in Adana in southern Turkey, told the BBC: "We need strong work gloves to move that rubble by hand. Because once they hear somebody alive in there, all heavy machinery stops and they have to dig in with their hands, and that just is beyond human capabilities.
"You need hands on site, and you need gloves for them."
How is the end time of an operation decided?
This decision is taken between the UN co-ordinating agency and the host country's central and local government.
The search and rescue attempts are usually called off between five and seven days after a disaster, once no-one has been found alive for a day or two.
However, people have been known to be rescued alive beyond this point.
In 2010, a man was found alive after a reported 27 days trapped under the rubble, following an earthquake in Haiti.
In 2013, a woman was pulled from the ruins of a factory building in Bangladesh, 17 days after it collapsed.