Sixty-four-year-old Nevada resident Stephen Paddock opened fire on an open-air country music festival on the Las Vegas strip on Sunday, killing at least 59 people, and injuring more than 500.
The shooting began at around (0500 GMT).
Las Vegas authorities called for blood donations over social media, urging people to attend designated blood banks rather than local hospitals, which remain overloaded after admitting more than more than 400 victims of the attack.
The residents of Las Vegas instantly responded to the calls. In the early hours of the morning after the shooting, hundreds of people lined up at blood banks, with many reporting on social media that their local bank was completely full.
Reporter David Schuman posted a video to Twitter, saying that at 3:48am, the blood bank on West Charleston Boulevard was completely full with people wanting to donate and help:
Erik Hill, the regional director of United Blood Services, said that he noticed people lining up in the carpark of the Charleston donation centre from around 2am, and has been drawing blood since 4am:
Other residents also tweeted their amazement and appreciation about the amount of people who showed up to donate blood:
United Blood Services posted a message of gratitude on their Facebook page, reminding people to continue to donate over the next few weeks so blood is readily available to those who are injured: