Orlando, Florida's gay community is in "utter shock" after falling victim to the worst mass shooting in U.S. history, a local LGBTQ leader said as national LGBTQ groups expressed immense heartbreak over the massacre.

At least 50 people were dead and 53 others were in hospitals after a gunman opened fire and took hostages at Pulse nightclub in Orlando.

Related: Florida Nightclub Massacre Is Deadliest Mass Shooting in U.S. History

Rob Domenico, a board member of The Center Orlando, an LGBTQ advocacy and support center, said "absolute devastation" is being felt across Orlando's LGBTQ community.

"Fear of the unknown is more overwhelming to us than anything, not knowing who of our loved ones is potentially laying on the floor dead," he said.

The shooter was identified as Omar Mateen. His father, Mir Seddique Mateen, told NBC News that his son got angry when he saw two men kissing in Miami a couple of months ago. He thinks that may be related to the shooting.

Related: Mass Casualties After Gunman Opens Fire in Gay Club

The Morning Rundown Get a head start on the morning's top stories. This site is protected by recaptcha

"We are saying we are apologizing for the whole incident. We weren't aware of any action he is taking. We are in shock like the whole country," Mir Mateen said.

Rep. Alan Grayson, D-Florida, whose district includes the area of the massacre, said the attack was "more likely than not ideologically motivated."

"It's no coincidence that the attack took place where it did and where it did," he said. "It might be that we've seen the commission of an awful hate crime."

Local organizations, both LGBTQ and non-LGBTQ, were coming together to offer their support, according to Domenico, and The Center Orlando was setting up counseling services where clergy and licensed counselors would be on hand to provide support to survivors.

PHOTOS: Gunman Opens Fire at Orlando Nightclub

"This is a time, more than ever, that we need to put the 'unity' back in 'community' and to stand up to show love and compassion to those going through this horrible travesty. ... Step out of your comfort zone," Domenico said.

"If you've never volunteered, now is the time you're needed," he added.

LGBTQ clergy leaders scheduled a vigil for Sunday night, followed by a gathering of Muslim and LGBTQ leaders to condemn the violence.

Equality Florida said the group was "reeling" from the news, and set up a GoFundMe page for the victims.

Related: Gay Blood Ban Still in Effect in Orlando

"Gay clubs hold a significant place in LGBTQ history. They were often the only safe gathering place, and this horrific act strikes directly at our sense of safety," Equality Florida said.

"Our hearts break for the victims and families of this horrific act of violence. We stand in solidarity with the LGBTQ community in #Orlando," the Gay & Lesbian Alliance Against Defamation (GLAAD) said in a Tweet.

My heart aches to release such a sad statement. Orlando LGBT community and leaders being held in our prayers! #hope pic.twitter.com/btw7HZCPeG — Stuart Milk (@StuartMilk) June 12, 2016

Chad Griffin, president of the Human Rights Campaign, the nation's largest LGBTQ civil rights group, said he was "devastated."

"This tragedy has occurred as our community celebrates pride, and now more than ever we must come together as a nation to affirm that love conquers hate," Griffin said.

President Barack Obama said Sunday: "This is an especially heartbreaking day for all our friends — our fellow Americans — who are lesbian, gay, bisexual or transgender. The shooter targeted a nightclub where people came together to be with friends, to dance and to sing, and to live.

"The place where they were attacked is more than a nightclub — it is a place of solidarity and empowerment where people have come together to raise awareness, to speak their minds and to advocate for their civil rights," Obama said.

Follow NBC OUT on Twitter, Facebook and Instagram.