Normal communications were cut off, roads were blocked by rubble and trees, electric power was interrupted and water was in short supply. The only lights visible in the city came from solar-powered traffic signals.

Among the public buildings that collapsed were the main parliament building, tax headquarters and prison along with schools and hospitals. Haiti's president, René Preval, said he had nowhere to go after both the presidential palace and his own home were destroyed.

Haitian Senate President Kelly Bastien was rescued from the wreckage of the parliament building and taken to a hospital in the neighbouring Dominican Republic. The headquarters of the UN, whose 9,000 peacekeepers have been stationed in Haiti since 2004 when President Jean-Bertrand Aristide was ousted, was also demolished.

As many as 100 UN staff – including the mission head and his deputy – remain missing and 36 have so far been confirmed dead. For the global organisation, it represented the greatest loss of life in single event in its history.

The archbishop of Port-au-Prince, Monsignor Joseph Serge Miot, was found dead in the wreckage of the archdiocese office.

Archbishop Bernadito Auza, the apostolic envoy to Haiti, said: "The cathedral, the archbishop's office, all the big churches, the seminaries have been reduced to rubble."

The lack of infrastructure meant that rescue workers and medical staff struggled to reach those trapped as well as basic supplies to treat the injured.

Elisabeth Byrs, spokeswoman of the United Nations Office for the Co-ordination of Humanitarian Affairs, said that relief agencies faced a "major logistic challenge" on the ground.

Paul Garwood, of the World Health Organisation, said at least eight hospitals and health facilities in and around the city had been damaged or destroyed.

"Roads are blocked by rubble, so cars, vehicles, ambulances can't reach those in need," he said. "WHO staff, for example, are going by foot to the central drugs store to get essential medicines and take them to health facilities."

John Andrews of the Pan American Health Organisation, said the lack of infrastructure meant that it was even more vital for rescue workers to co-ordinate their efforts.

"We urge donors and relief organisations to keep in mind the importance of rebuilding Haiti's infrastructure and keep them safe for future disasters," he said.

"We ask that all field hospitals should be fully self-sufficient and should not request any support from the affected community."

Haiti has no real construction standards and Port-au-Prince's mayor estimated a year ago that 60 per cent of the capital's structures were unsound. The Government, which is propped up by international aid, was due to launch an investigation into property safety just before the earthquake struck.

The destruction of the capital also means that legislative elections planned for next month, and a presidential election planned for November, will also have to be put on hold – potentially provoking further unrest.