New York  - The United Nations launched Monday a long-planned and ambitious programme to completely renovate the ageing building that has served as its world headquarters in the past 60 years, with pledges to make it an example of stewardship in the environment as well as efficiency.

UN Secretary General Ban Ki-moon, flanked by senior aides and representatives of major UN organs, broke ground in the large garden that is part of the complex, where a temporary building will be erected for conferences, activities and offices.

The renovation will take at least five years to complete, which will mean the relocation of most of the 4,500 UN personnel to office spaces already rented in New York City.

The costs will be 1,8 billion dollars, supported by UN members as long-term, low interest loans.

It will involve the relocation of hundreds of journalists from world media covering the UN to temporary space office within the compound, unlike UN staff who will have to work in buildings away from the headquarters.

The UN headquarters is visited by about 1 million people a year, most of them tourists from around the world.

"Over five years, we will make our facilities safer and more modern," Ban said before he and guests donned construction hats and dug up shovels of earth in the green grassy area known as North Garden.

"We will make them greener and more efficient," he said. "We will make then a model of environment (and) of stewardship, by reducing our electrical and water usage, and by removing harmful materials that were used in the original construction."

Michael Adlerstein, chief of the renovation programme, told reporters he and his team of architects and builders are confident they will complete the task by 2013.

"The UN will look just like it is today, five years from now," he said. "It will be a very functioning building, not fancy, but very efficient."

The current UN headquarters, which opened in the early 1950s after the cornerstone was unveiled on October 24, 1949, has violated all safety building codes of the United States, including building materials that include asbestos and fragile heating pipes.

Fire detectors were first installed only in 2007 in some areas, including the third and fourth floors used by the media. Fire drills were practiced only in recent years.

When the compound was opened in the 1950s, the United Nations had 70 members and a small staff. There are today 192 members, who demand more support from a secretariat of workers hired from all countries around the world.

The original building was designed by an international team headed by French architect Le Corbuisier. It was constructed on a 18-acre of land donated by the Rockefeller family along Manhattan's East River. dpa