Traumatised victims and witnesses of the terrorist attacks on the US could take months or years to recover from the psychological impact of their ordeal.
Experts said survivors of the disaster, bereaved relatives and even those who simply watched the carnage on television could require help in coming to terms with their distressing experiences.
Dr Michael Isaac, a consultant psychiatrist at London's Maudsley Hospital and a senior lecturer at King's College in London, warned that people across the world would now be at risk of post-traumatic stress disorder.
"Anyone who has watched the pictures on TV can hardly fail to be affected by it," he said. "Once people go beyond shock they often develop post-traumatic stress disorder (PTSD). People will re-experience the trauma through repeated nightmares or daytime flashbacks.
"They will also become extremely over-vigilant. If they hear a loud bang or aircraft flying overhead they will jump out of their skin. I think many British people will have a lot of difficulty getting these horrific images out of their minds. PTSD can go on for years – some may never get over it."
At New York hospitals, medical staff said yesterday that counselling people for delayed shock and deeper psychological damage would be a major priority. At least three hotlines to help people with mental health problems have been set up.
The American Red Cross is also offering counselling to the public and emergency services staff. "We have been preparing for something like this for quite some time – even before the Oklahoma bombing," said spokeswoman Tracy Gary.
Many aspects of the attack – including its suddenness, the terrifying scale, the sophistication of planning, the use of suicide bombers and the way it was recorded on film – will add to the mental scars.
Leslie Carrick-Smith, a psychologist and trauma specialist from Chesterfield, said: "The scale of this is bigger than anything anyone has ever seen in a lifetime. What is so potentially psychologically damaging about it is its unexpected nature.
"Nobody is really going to feel safe because those towers were icons, symbols of world commerce and order. People realise how vulnerable they are to whoever could actually do that," he said.
Pamela Dix of Disaster Action, a British support group for relatives who lose family members in disasters, said: "It is going to be a long uphill climb, dealing with a disaster so monumental. People will need their strength for the future. There is no going back to the way life used to be."
Ms Dix, whose brother Peter was killed in the 1988 Lockerbie bombing, had a three-hour wait on Tuesday before hearing that another brother, who lives in Manhattan with his family, was safe.
Professor Anke Ehlers, a psychiatrist from the Centre for Anxiety Disorders and Traumas at the Maudsley Hospital, said that initially everyone would be in a state of "shock and disbelief". Later those more closely involved in the catastrophe could start to suffer disturbing flashbacks of what they had seen, experience problems sleeping or concentrating, display irritability or feel permanently on edge.
About 75 per cent would get over these symptoms in the course of time but the rest would probably need some psychological help to overcome their trauma. People who escaped the buildings and officers from the emergency services may also suffer intense guilt that they had survived and left behind others who died.
She added that many people would feel generally threatened by another terrorist attack or other serious mishap. "While they felt safe at home and work before, they may develop an over-generalised sense of danger. They may feel like they have a 50 per cent chance of being killed from one day to the next even though the probability has not changed."
Children who had obvious fears should be encouraged to talk about them but others should be reassured that Tuesday's assault was a one-off.Reuse content