NEW YORK (AFP) - New York City's Empire State Building went dark late on Sunday (June 12) while the spire of One World Trade Center lit up in the colors of the gay pride flag in memory of the victims of the Orlando massacre.

The symbolic move came as the United States mourned the 50 victims of the worst mass shooting in modern United States history, gunned down at a gay club in the Florida city.

In the wake of the attack by a heavily armed assailant, New York Mayor Bill de Blasio announced that all flags would be flown at half-staff in the largest US city and that security measures have been strengthened, in particular around places associated with the LGBT community.

Mr De Blasio told reporters that the shooting that also left dozens injured was "against our values". He said there were no credible threats directed at New York City.

But "you'll see a lot of additional police presence on the streets of the city", he added, stressing: "No city in the world is better prepared to stop terror, to stop hate."

Hundreds of people gathered on Sunday evening in Greenwich Village to reflect on the violence and leave flowers, candles and letters beside a sign reading "Stop Hate".

The Tony Awards, which honor the best of Broadway, opened in New York dedicated to victims of the shooting, the deadliest terror attack in America since Sept 11, 2001.