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People have been lining up to give blood at donation centers around Las Vegas since the early hours of Monday morning following the deadliest mass shooting in U.S. history.
At least 58 people were killed and more than 500 wounded after a lone gunman opened fire on the crowd at an outdoor country music festival on Sunday night. People immediately began to head to donate blood in Las Vegas upon hearing the news.
The shooting occurred during a performance by country music star Jason Aldean when a gunman opened fire from the 32nd floor of the Mandalay Bay Resort and Casino, police said.
"What we ask for is blood," Las Vegas Mayor Carolyn Goodman said during a news conference Monday morning. "Please donate blood."
United Blood Services has sent nearly 200 units of blood and blood products to the Las Vegas hospitals treating shooting victims, said Julie Scott, senior director of strategic donor marketing. The American Red Cross has provided more than 250 additional blood products and is ready to send more as needed, the organization said in a statement.
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The response to calls for blood donors was swift. Donation centers had already begun filling up by 4 a.m. with people eager to help.
A list of places to donate blood in the Las Vegas area has also been disseminated, and the Las Vegas Metropolitan Police Department also listed a place to donate.
City officials in Las Vegas have created a hotline in which those looking for updates and information on family and friends can call 1-866-535-5654. They also set up the Metro headquarters as a reunification center.
United Blood Services and University Medical Center in Las Vegas announced blood drives beginning early Monday morning local time. Uber is providing free rides to and from blood donation centers and hospitals, NBC affiliate KSNV reported.
"We are seeing tremendous response from the community with potential donors already lining up to give blood," Scott told TODAY.
Make an appointment to donate blood even if you don't live in Las Vegas, the Red Cross urged. Blood donations will become part of the national blood inventory, helping to ensure it's "prepared for any blood needs that arise wherever blood is needed." Visit the Red Cross website or call 1-800-RED CROSS to set up an appointment.
"Blood has a shelf life, so it is important that donations are given on an ongoing basis. We understand that people want to come forward now to show their support, however, to effectively manage the blood supply for patients, we are asking donors to make appointments to give blood throughout the coming days and weeks," Scott added.
Making the need for blood particularly acute is that United Blood Services announced in July that it was suffering a severe shortage. Stocks of O-negative and B-negative blood were so low that it had to ration blood among 24 hospitals in the Las Vegas area.
At this point, the Las Vegas operations of United Blood Services have been able to provide enough blood needed by hospitals treating victims, Scott said.
TODAY's A. Pawlowski contributed to this report.
Follow TODAY.com writer Scott Stump on Twitter.