UN Secretary General Ban Ki-moon has appealed to frustrated Haitians to be patient over efforts to bring them relief from last Tuesday's earthquake.

Aid workers say relief efforts are being slowed by bottlenecks, but food and water are finally reaching some parts of the capital Port-au-Prince.

Survivors of the earthquake have become desperate as they wait for aid.

Many are trying to leave the city, and there are security concerns amid reports of looting.

Lt Gen Ken Keen of the US Southern Command said that while streets were largely calm there had been an increase in violence.

The AFP news agency quoted one of its photographers as saying police had opened fire on looters in a Port-au-Prince market, killing at least one of them.

Feeding 'challenge'

Mr Ban spoke in Port-au-Prince after visiting the ruins of the UN mission, where several senior UN staff were killed. Among the dead were the special representative and his deputy. Hundreds of staff are still missing.

However, one Danish UN worker was pulled alive from the rubble of the building on Sunday afternoon. Four other people were rescued in Port-au-Prince during the day.

"I appeal to the Haitian people to be more patient," Mr Ban said, after seeing hungry and homeless people vent their frustration outside.

He added that he knew people were angry, but said deliveries of aid were now being made in a more efficient and co-ordinated manner.

He said providing daily food to two million people, as the UN has pledged, would be a "huge challenge".