The funds are intended to help three million people over six months, said UN humanitarian chief John Holmes.

He said almost half of the appeal money would be for emergency food aid, with between US$20m and US$50m allocated for healthcare, water, sanitation, emergency shelter, early recovery and agriculture.

About $360m has been pledged so far to the relief effort, but only part of this sum will be included in the emergency appeal.

Mr. Holmes earlier told reporters that 30 percent of the buildings in Port-au-Prince had been damaged, up to 50 percent in some areas.

Many there have spent a third day without food and shelter in the ruined capital, though UN Secretary General Ban Ki-moon, who is due to visit Haiti on Sunday, said the distribution of food and medicine was under way.

In response to the appeal, a hospital ship and more helicopters are due to arrive in the upcoming days, carrying more troops and marines, the total number of US troops is expected to rise to between 9,000 and 10,000.

Plane-loads of rescue workers and relief supplies have arrived or are due from the UK, China, the EU, Canada, Russia and Latin American nations.

Gen Douglas Fraser, the commander of US Southcom, says around 90 aid flights everyday are landing.