As more than 500 wounded flooded the hospitals of Las Vegas after the worst mass shooting in modern US history, electronic billboard ads urged people to give blood.
The response from the community has been overwhelming, with long lines of donors snaking out the doors -- sustained with offerings of pizza and cookies.
"Donors came after two in the morning when they received the news. The flow did not stop well until the evening," said Mitzy Edgecomb of United Blood Services, an agency that collects donated blood and supplies it to hospitals.
"Yesterday we collected 700 donations in the Las Vegas area. Well over 1,000 people attempted to donate. We are seeing numbers not seen in a very long time," Edgecomb said outside a blood drive center in suburban Las Vegas.
Tuesday morning, when the doors opened at 9:00 am, more than 100 people were waiting outside to give blood, and in the afternoon a dozen were still waiting.
A Salvation Army truck handed out free slices of pizza.
People not even wishing to donate showed up with water and homemade cookies.
"Anything like this brings a community together. People are good at heart and they want to do something to help at the time when they are slightly helpless," said Edgecomb.
She said she expects the flow to keep up through the weekend.
"We've met the needs at the hospitals where some of the victims were transported. We are replenishing that supply and preparing for the days and weeks ahead," she said.
'We love you'
At one blood drive center, Dianne Spence, 70, lay down on a cot next to her husband Richard.
She squeezes a rubber ball as a nurse inserts a needle into her arm. She is from Georgia and has lived in Las Vegas for 27 years.
She is a regular blood donor and already had an appointment for Tuesday, even before Sunday's carnage by a retired accountant named Stephen Paddock. He killed 58 people and himself, and wounded 527.
Spence kept her appointment "because it is a critical time and people need it."
She said she was proud of the way the people of Las Vegas are responding to this crisis.
"Hate is just a sad symptom of fear. People are in a very rough place today," she said. "I grew up in the south and we have a lot of hate. It's just sad, really sad."
One cot further over, Sammy Rangel is talking to the nurses.
He is wearing a T-shirt with the slogan "Las Vegas, We Love You" that does not quite hide all the tatoos on his body.
Rangel used to be the leader of a white supremacist gang in Chicago and spend 18 years in prison.
Then he founded an association called Life after Hate, which brings people like him together for social rehabilitation programs.
The motives of the shooter in Las Vegas are still not known.
Rangel said he is here to "counter the message of hate with love and compassion." And blood donations.
"This is where acts of hate and terror lose, because they're not designed to bring communities together and yet it seems that when these things happen, communities come together," said Rangel.
"It's counter-intuitive to what they're trying to accomplish, right?"
Douglas Fraser, a surgeon at University Medical Center, said he saw more than 100 patients come in after the shooting, including 20 in critical condition.
He said his people are trying to help both physical and psychological injuries, and the latter take longer to heal.
"The emotional strain is probably the highest right now," he said. "Right now we are just trying to help each other and the patients kind of get right through this."
"Some of these wounds will heal physically but the mental aftermath is going to be for some time," he said, adding victims' families members of would also have to deal with the trauma of mass shooting.