A crowd flying rainbow flags came together in downtown Orlando to pay their respects to the 49 people killed in the attack on a local gay club.

Families with small children were also among mourners outside a performing arts center, leaving flowers, candles and notes at the makeshift memorial.

Many of the people said that the popular Pulse nightclub played an important role in their lives as gays and lesbians.

"Pulse gave me confidence, made me realize I was normal and so much like everyone else," said Cathleen Daus, a former employee at the venue.

Commenting on the hate crime, art student Alex Hartdegen said that people should learn to accept everyone, even if they disagree with their decisions.

"It's none of your business what other people do with their lives or how they love people or who they love," she said.

Several Pulse visitors told the Orlando Sentinel newspaper that the shooter was himself a regular guest at the gay bar.

"Sometimes he would go over in the corner and sit and drink by himself, and other times he would get so drunk he was loud and belligerent," Ty Smith told the paper on the shooter Omar Mateen.

Another Pulse patron, Kevin West, told the Los Angeles Times that Mateen messaged him repeatedly via a gay chat app.

'We stand with you'

Thousands of people also turned up for the vigil in New York, where the city's mayor Bill de Blasio and state governor Andrew Cuomo vowed to fight discrimination.

The mayor said he would make New York safe for everyone, including LGBT people, Muslims and Latinos – as Latinos appeared to be the majority of the victims.

"We stand with you, we will protect you," De Blasio told the crowd near the historic Stonewall Inn, the birthplace of US gay rights movement.

"We are all New Yorkers, we are all Americans and yes, we are all Orlando."

The Manhattan crowd chanted "Love beats hate," holding hands and hugging, under banners for the upcoming Pride Week event.

Student Erin Kohler, president of Ithaca College Queer Club, said that the vigil was an opportunity to bond, and "watching this whole community become one."

She added that she supported restrictions on the sale of semi-automatic weapons, despite being an NRA member and a competitive hunter.

"I just don't understand the need for assault rifles, there's no reason," she said.

Gay couple detained in Moscow

Similar mourning events were held in dozens of US cities and many places across the world. In London, gay bars in Soho closed for one hour late Monday to mark the shooting, while Paris draped its town hall in rainbow flags.

People in Berlin placed flowers and candles in front of the US embassy, with a separate event also honoring the victims in the western city of Cologne, known for its gay scene.

Tributes were also left before the US embassy in Moscow, alongside a rainbow-colored flag. A gay couple, however, was detained while trying to leave flowers and a sign reading "Love wins - Stay with Orlando," according to Russian RBC media group.

Islam Abdullabeckov, who works as social media editor in RBC, said the police arrested him and his boyfriend Felix Glyukman over "unauthorized action."

"We only wanted to express our condolences for the murder of these people and we had not at all planned any kind of political act," he added.

The two men have been charged with disobeying procedure for holding public events. Both of them have since been released. The RBC media group has bumped heads with the state in the past over their criticism of President Vladimir Putin.

Russia's LGBT community is struggling against widespread homophobia. Gay and lesbian activists may face prison time under the country's controversial law banning "gay propaganda."

President Putin, however, joined the condemnation of the Orlando killings, decrying them as a "barbaric crime."