Haiti, the poorest country in the Western Hemisphere, presents unique logistical challenges for aid workers even in the best of times. It shares an island with the Dominican Republic, meaning that aid must arrive by sea or air. Haitian streets are in poor condition under normal circumstances, and even if aid reaches the Dominican Republic, the road from there to Port-au-Prince is narrow and easily clogged.
Almost everything has to be imported, even wood for building temporary shelters, because Haitians have denuded their hillsides by cutting trees for cooking fuel.
"If you see Dominican Republic and Haiti from the air, it's really striking," said Byrs. "Half of the island is green and the rest is dust."
In addition, Haiti was already heavily damaged by a series of severe hurricanes, the most recent in 2008.
President Barack Obama announced Thursday the U.S. government was making an initial $100 million relief effort and promised an all-out rescue and humanitarian effort that included military and civilian emergency teams from across the U.S.
"We have to be there for them in their hour of need," Obama said.
The aircraft carrier USS Carl Vinson was deployed to Haiti, and the amphibious assault ship USS Bataan had been ordered to sail as soon as possible with a 2,000-member Marine unit.
Even as the United Nations stepped up its massive aid operation, the world body was trying to determine how many of its own staff were killed in earthquake.
"It's very difficult to give an exact number," Byrs said. "This is also a tragedy for the United Nations."
She said up to 100 U.N. staff were trapped in the main U.N. peacekeepers' building, which was destroyed.
Byrs said the U.N. believes there is a good chance many people are surviving in the rubble and might be saved.