Thousands of people have died after a strong earthquake that hit Turkey and Syria on Monday.
A search and rescue operation is underway, with specialist teams from all over the world.
However, people in some hard-hit areas say rescue efforts are 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 people trapped.
They do this by looking for “voids” – spaces under large concrete beams or stairwells where survivors can be found.
The possibility of further collapse of a building must also be considered, as well as other hazards such as gas leaks, flooding and hazardous objects, such as asbestos in roofs.
While rescuers try to reach survivors, support workers watch for construction movements and listen for strange noises.
Buildings that have completely collapsed are usually searched last, because the chances of finding survivors are very small.
The work of rescue teams is coordinated by an agency, usually the United Nations (UN) and the host country. Rescue workers are specially trained and work in pairs or larger teams, while local people are often involved.
What rescue equipment is needed?
To move the rubble, rescue teams use heavy machinery, including excavators and hydraulic jacks.
Large concrete slabs on the outside of buildings can be pulled aside by excavators, allowing rescuers to see any people trapped inside.
Video equipment on the end of flexible poles can be passed through openings to help locate survivors.
Specialized sound equipment can detect the faintest sounds to within a few meters. Silence on the site is called for as a member of the rescue team strikes three times, hoping 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 higher concentration of CO2 in the air exhaled by those still breathing.
Thermal imaging equipment can be used to locate people who are not directly in a rescuer’s line of sight, as their body heat can heat up the debris around them.
What do the rescue dogs do?
Using their sense of smell, specially trained dogs can pick up signs of life where human rescuers cannot.
Dogs can also cover large areas quickly, speeding up the search and rescue process.
Should people use their bare hands?
Once the large slabs and structures are removed, rescue teams use their hands and small tools such as hammers, picks 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 when removing sharp pieces of debris.
However, in some parts 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 as soon as they hear someone is alive, all the heavy machinery stops and they have to dig with their hands, and that is simply beyond human capabilities.
“You need hands on site, and you need gloves for them.”
How is the end time of an operation determined?
This decision is made between the coordinating UN organization and the central and local government of the host country.
Search and rescue efforts are usually called off between five and seven days after a disaster, if no one has been found alive for a day or two.
However, people are known to be rescued alive after this point.
In 2010, a man was found alive after reportedly being trapped under the rubble of an earthquake in Haiti for 27 days.
In 2013, a woman was pulled from the ruins of a factory building in Bangladesh 17 days after it collapsed.