The Empire State Building was dark on Sunday night, while One World Trade Center displayed the colors of Pride.
Cities across America are paying tribute to the 49 victims gunned down inside an Orlando nightclub early on Sunday.
On Sunday night, the Empire State Building's lights were switched off out of respect for the victims, while the colors of the rainbow were displayed on One World Trade Center in a sign of solidarity with the LGBT community. Pride flags were also unfurled outside City Hall.
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Mourners gathered in front of the West Village's Stonewall Inn, which is considered the birthplace of the gay rights movement. A vigil will be held at the bar on Monday night, and Governor Andrew Cuomo and Mayor Bill de Blasio are expected to attend.
"This senseless act of terror reminds us that there are those who seek to undermine these very values and the progress we have achieved," Cuomo said in a statement on Sunday. "We will not let this happen.
"An attack on one is an attack on all. New York joins the rest of the nation in rejecting this hate, fear and extremism and stands shoulder to shoulder with the LGBT community."
President Barack Obama ordered U.S. flags to be flown at half-staff at all federal buildings, including the White House and embassies around the world, until Thursday.
Mourners also gathered at vigils across cities including Seattle and Chicago.
Brian Johnson, the CEO of the Chicago-based gay rights organization Equality Illinois, said an attack at a gay bar held particular significance for the community.
"We are not a community that had churches to congregate in," he told AFP. "An attack on us in a nightclub is not just an attack in a place where we socialize, it's an attack in the center of the community where we feel safe."
In Florida, hundreds lined the streets to donate blood for those still fighting for their lives in hospitals.
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Following the attack, blood agency OneBlood and the Orlando Regional Medical Center urged people to donate. OneBlood spokesperson Pat Michaels said they are looking for healthy donors older than 16 who weigh at least 110 pounds.
There were lengthy lines in the street as people waited to donate to OneBlood.
But there's also renewed outage that sexually active gay men are not allowed to donate blood; the FDA prohibits any man who has had sex with another man in the last year from donating.
A candlelit vigil was also held in the streets of Rome, while in Paris, which suffered its own tragic attacks last year, dozens of mourners paid their respects while brandishing signs expressing their support. "We have love," one sign read.
Government buildings across the world were lit up with the colors of the rainbow flag.
On Monday, authorities confirmed that 49 people were killed in the attack at the Pulse nightclub in Orlando. The gunman was also killed.
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