A gunman who barricaded himself with hostages inside a Florida apartment complex has killed six people before being shot dead, Sky News reported.

Police said the hours-long standoff, which began at 6.30pm local time, in a five storey building in Hialeah, just north of Miami, ended with the gunman being killed by a SWAT team.

The bodies of three women and two men were found in the apartment complex after police arrived. Another man was killed across the street when the gunman allegedly spotted him and took aim.

Two of the hostages the man took were reportedly unharmed.

Before the shootout, police had been able to communicate with the gunman. Officers are still investigating the motive and identifying the gunman and victims.