Having looked to the Manhattan skyline and seen their city under attack, New Yorkers by the thousands flocked to hospitals, rolled up their sleeves and gave their blood, hoping to help the wounded and the dying.
One was Noah Kaufman, 40, a project design manager for the city. With the subways closed, he walked for miles to reach Elmhurst Hospital Center.
"As soon as I realized the extent and realized the buildings had collapsed, I knew they would need blood," Kaufman said.
He was angry.
"These are chickens," he said, before leaving the hospital. "You don't blow up innocent people just because you're mad at this country."
Area blood centers, which usually must plead for donors, were overwhelmed by people wanting to help.
The New York Blood Center's network of collection sites in New York and New Jersey had gathered about 4,000 units by 5 p.m., twice what it usually takes in, according to Rachel Singer, the center's assistant to the president.
"We've been inundated," Singer said.
Singer said that although the blood shortage of the early summer has abated, a new blood shortage could strike immediately. She said there remains a need for donations from people with O-negative blood - known as universal donors - and urged potential donors to call 800-933-2566 for information on where to give.
Donor centers at hospitals everywhere were overwhelmed.
At Elmhurst, which usually devotes three beds for blood donors, doctors squeezed almost a dozen additional stretchers into a makeshift ward. More than 150 donors waited for more than two hours in the auditorium before hospital authorities began turning them away.
Some were frightened. Some appeared to be in shock.
Gene Baez, 53, a Jackson Heights retiree, looked about vacantly as he waited to donate, wondering whether his two nephews were safe. They attend school near the financial district, he said.
Kathleen O'Malley, 19, of Springfield, Va., was one of many St. John's University students who came to Elmhurst to give blood. She and other students had watched from the hilltop campus in stunned disbelief as the towers crumbled.
In a makeshift ward set up at the Elmhurst Hospital Center, a woman lay on a stretcher, a tube snaking red from her arm to a plastic receptacle. Her eyes were rimmed in red.
"You just think of the people who worked there and hope they got out," said the woman, who did not want to give her name. "I have cousins and nephews who are cops and firemen. One is a fireman at the South Street Seaport. One is a policeman in the First Precinct. They would have been there."
At New York Presbyterian Hospital, potential donors were being turned away by 1:30 p.m. Officials were taking names and urging them to return today.
Fifteen Yeshiva University students - all type O - who had walked a mile to the hospital promised to recruit more type-O students and return today. "I'm just trying to give a helping hand," said Adam Richards, 20, a junior from Atlanta.
"It's important that New York band together. It's the right thing to do. It could have happened to you."