UPDATED: Authorities say about 20 people have been killed and more than 40 injured in a mass shooting at a gay bar in Orlando, Florida.

“I don’t want to give anyone a number right now, but there are multiple people dead inside the nightclub, and at least 42 people have been transported to various hospitals,” Orlando police chief John Mina told a press conference.

Mr Mina said police were called to the Pulse nightclub about 2:00am on Sunday (local time) after reports of gunfire.

He said the gunman exchanged gunfire with an officer and then went back inside and took hostages.

He said the “lone wolf” gunman was armed with an assault rifle, a handgun and an unspecified “device”.

“It appears he was organized and well prepared,” Mr Mina said, adding that the gunman was not from the Orlando area.

The gunman was killed during another shoot-out with authorities about three hours later during an operation to rescue the hostages, Mr Mina said.

The night club shooting happened just a day after a man shot dead singer Christina Grimmie while she was signing autographs following her concert in Orlando.

Mina said there was no indication of a link between the two shootings.

– with other agencies