The main airport in Indonesia's tsunami hit Banda Aceh, a key hub for relief flights, was closed all day Tuesday after a chartered Boeing 737 hit a water buffalo on the runway damaging its landing gear in the early hours of the morning.

Helicopters continue to fly in and out of Banda Aceh's airport, delivering aid desperately needed in far-flung areas on Indonesia's northern island of Sumatra.

But other air traffic was stalled after a chartered jet hit a water buffalo on the runway, closing the airport till late afternoon.

Chief Warrant Officer Rick Truelove, head of the U.S. military disaster relief team here, says the plane mishap could not have come at a worse time.

There was just enough aid to last for one day, and more supplies needed to be brought in from Sumatra's relief hub of Medan.

"We're still moving cargo and supplies," said Mr. Truelove. "The challenge we've got right now is we've got all of the humanitarian assistance supplies stock piled down at Medan and the issue right now is getting from Medan up here."

The runway was eventually cleared. But the water buffalo incident illustrates just one of the many problems the unprecedented relief operations here are running into.

Access is a huge obstacle. The December 26 tsunami, which killed some 100,000 people in Indonesia alone, took out most of the roads, infrastructure and left the region without government officials and volunteers.

While hundreds of foreign relief workers are here in the world's biggest-ever response to a natural disaster, figuring out where people are in most need and bring aid to them remains a daunting task.

Chief Truelove says he went out to survey the Banda Aceh port to see if ships could also deliver relief, but found it unusable.

"Basically the pier structurally is not sound," he concluded. "Underneath you can see where it's buckled the cement so we definitely have to do some structural work to be able to bring anything over that pier. We're looking at other beaches and ports and as soon as we can identify one that we don't have to rebuild completely, we'll have another option bringing things in by surface."

Relief officials say nearly two million people in the 12 affected countries along the Indian Ocean are in need of food assistance and help to ward off the threat of disease.

Here in Banda Aceh Tuesday, thousands of shocked survivors of the tsunami stood in long lines in front of the destroyed mall queuing for water at an aid station set up by Indonesian businessmen.