But time moves very fast for anyone caught in debris after an earthquake.

The survival time of people who are trapped under collapsed buildings varies greatly on the time of year, the terrain and the physical injuries they have suffered.

A basic rule of thumb is that if they are not rescued within 48 hours, there is a 90% chance that they will not live.

There are exceptions, like the little boy found on Friday morning in Tali.

Most people, however, succumb to dehydration, whether or not they are suffering from physical injuries.

Dr Michel Thieren, medical officer for the WHO's humanitarian assistance programme, said: "You don't need to be in a critical condition to be at risk of dying after three days without drinking anything."

Lack of oxygen can also be a problem.

Speed is vital

Those who are rescued often need rapid medical attention.

The first thing that doctors need to do is to assess the patient for head injuries, and damage to organs.

This can be done by testing reflexes, measuring blood pressure and assessing level of awareness by asking simple questions.

At this stage it is also important to dress minor wounds, which if left untreated may become infected.

Most people who have been trapped under rubble also need treatment to bring their body fluids up to more normal levels.

This can be done by administering rehydration salts, water, and in serious cases a glucose drip.

Crush syndrome

Rescue teams have to work fast to find victims in time

One of the most common problems is a condition known as crush syndrome. This must be treated with 48 hours otherwise it can be fatal.

When the muscles are crushed they release a protein which in normal circumstances is entirely harmless.

However, once the protein is released into the blood stream it finds its way to the kidney, where it can block the function of the organ and lead to total kidney failure and death.

People with crush syndrome need to receive kidney dialysis as soon as possible so that their blood can be purged of the toxic protein.

The relief organisation Medicins Sans Frontieres (MSF) has sent one kidney specialist and five specialist nurses to the earthquake disaster zone to tend survivors.

Psychological care

Once a patient has been stabilised, it is important that they also receive psychological care as quickly as possible.

MSF aims to provide psychotherapeutic care to victims within a week

MSF spokesman Nathan Ford said: "Psychological care is something that comes after more immediate medical care, but it is something that nevertheless has to be done pretty quickly.

"The longer you wait the more complex the problems can become. Stress can quickly turn into post traumatic stress disorder, and we try to nip the problem in the bud as quickly as possible."

MSF runs a programme of psycho-social care which is designed to help victims accept that they have suffered a traumatic experience, and then to achieve a rational perspective about what they have gone through.

These programmes take the form of 10-15 counselling sessions in the days after the disaster.

Other organisations use different techniques. For instance, Unicef provided art therapy for children caught up in the Kosovo conflict.