Police said "multiple" people were killed when a SWAT team moved early Sunday to rescue people taken hostage by a gunman at a gay nightclub in Florida.

"This did turn into a hostage situation," Orlando police chief John Mina told a media briefing. "At approximately 0500 hours (0900 GMT) this morning, the decision was made to rescue hostages that were in there."

"There are multiple people dead inside. I don't want to give a number right now," Mina said.