In what is becoming a regular occurrence, President Barack Obama has ordered that American flags be lowered for the victims of a mass shooting incident on United States soil.

On Sunday, June 12, the president issued a proclamation "as a mark of respect for the victims of the act of hatred and terrorism perpetrated on Sunday, June 12, 2016, in Orlando, Florida ... that the flag of the United States shall be flown at half-staff at the White House and upon all public buildings and grounds, at all military posts and naval stations, and on all naval vessels of the Federal Government in the District of Columbia and throughout the United States and its Territories and possessions until sunset, June 16, 2016.

"I also direct that the flag shall be flown at half-staff for the same length of time at all United States embassies, legations, consular offices, and other facilities abroad, including all military facilities and naval vessels and stations," the brief statement continued.

Hook & Ladder firefighters will be lowering the flag on Newtown's Main Street flagpole at 5 pm Sunday.

According to the Associated Press, a gunman wielding an assault-type rifle and a handgun opened fire inside a crowded gay nightclub early Sunday, killing at least 50 people before dying in a gunfight with SWAT officers, police said. It has been deemed the deadliest mass shooting in modern US history.

At least 53 people were hospitalized, most in critical condition, officials said. A surgeon at Orlando Regional Medical Center said the death toll following the incident at Pulse Orlando was likely to climb.

The shooter called 911 shortly before the attack and referenced ISIS, FBI agent Ronald Hopper said.

Authorities are investigating the attack as an act of terrorism.

The suspect exchanged gunfire with 14 police officers at the club, which had more than 300 people inside.

At one point, he took hostages, Police Chief John Mina said. Around 5 am, authorities sent in a SWAT team to rescue the hostages.

In addition to the assault rifle, the shooter also had some sort of "suspicious device," the police chief said.

In the immediate aftermath of the attack, police departments across the country stepped up patrols in neighborhoods frequented by the LGBT community.

Authorities were looking into whether the attack was an act of domestic or international terrorism, and if the shooter acted alone, according to Danny Banks, an agent with the Florida Department of Law Enforcement.

President Barack Obama called the shooting an "act of terror" and an "act of hate" targeting a place of "solidarity and empowerment" for gays and lesbians. He urged Americans to decide whether this is the kind of "country we want to be."

Associated Press content was used in the preparation of this story.