Orlando nightclub shooting: Police confirm gunman is dead after 'mass casualties' reported at Florida gay club

'More than 20 people' are believed to have been shot following the attack at Pulse

A gunman is dead and more than 20 people have been shot following an attack and hostage stand-off at a gay nightclub in Florida.

Orlando police said there were "mass casualties" at the Pulse venue following the attack in the early hours of Sunday morning.

More than 20 people were shot when the gunman opened fire in the nightclub at around 2am local time (7am UK time) before taking several people hostage, according to local media reports.

A post on the club's Facebook page from the time of the shooting said: "Everyone get out Pulse and keep running".

Witnesses described the gunman shooting at the ceiling and into the crowd at the packed club.

One witness, Ricardo J Negron Almodovar, told Sky News: "At around 2am someone started shooting. People just dropped on the floor. I guess the shooter was shooting at the ceiling because you could see all the glass from the lamps falling.

"There was a brief pause in the shooting and some of us just got up and ran out the back".

Another witness, Rob Rick, said it happened around, 2 a.m., just before closing time.

"Everybody was drinking their last sip," he said.

He estimated more than 100 people were still inside when he heard shots, got on the ground and crawled toward a DJ booth.

A bouncer knocked down a partition between the club area and an area in the back where only workers are allowed. People inside were able to then escape through the back of the club.

Dozens of emergency and police vehicles, including a SWAT team and a bomb squad, attended the scene and police detonated a controlled explosion outside the venue.

Local media reported there were fears the gunman could be wearing a bomb vest.

Amateur footage captured at the scene during the siege recorded the sound of shots being fired.

The motive for the attack is unknown.

Additional reporting by agencies