Omar Mateen has been identified as the gunman who killed at least 50 people when he opened fire in a crowded LGBT nightclub in Florida early on Sunday, the city's mayor and police said.
53 people have been injured and are being treated at the Orlando Regional Medical Centre.
Mateen, 29, lived in Florida and is an American citizen whose parents are from Afghanistan, CBS News reported citing law enforcement officials.
A senior FBI official said there were suggestions that Mateen might have had leanings toward DAESH but that this required further investigation.
Mateen entered Pulse Nightclub and started shooting at patrons and held others hostage.
"At ... 0500 hours this morning, the decision was made to rescue hostages that were in there. Our officers exchanged gunfire with the suspect. The suspect is dead," Orlando Police Chief John Mina told a press conference.
— Orlando Police (@OrlandoPolice) June 12, 2016
The dance club urged patrons to "get out" and "keep running" in a post on its Facebook page.
One witness claims she heard more than 40 gun shots fired back to back.
Those who were able to escape did so through the back of the club.
A “controlled explosion” was carried out by police at the club hours after the shooting broke out, but did not explain why that was done.
In a Twitter message, Orlando Regional Medical Center said it was placed on lockdown, with only essential workers and relatives of victims allowed access.
If you believe an immediate family member may be in the hospital, please come to the main entrance of ORMCs new north tower. ID required.
— Orlando Health (@orlandohealth) June 12, 2016
The new death toll that was given by Orlando Mayor Buddy Dyer to reporters has made the attack the deadliest mass shooting in US history, eclipsing the 2007 massacre at Virginia Tech university, which left 32 dead.
It was the second deadly shooting at an Orlando night spot in the last few nights. Late Friday, a man thought to be a deranged fan fatally shot Christina Grimmie, a rising singer and a former contestant on "The Voice", while she was signing autographs after a concert in the Florida city.