A confrontation between law enforcement agents erupted in gunfire Thursday evening at the federal building in Long Beach, leaving one dead and one seriously injured, authorities said.

The incident involved agents from the federal Immigration and Customs Enforcement Agency in the Glenn M. Anderson Federal Building along the city's oceanfront.

The shooter is believed to have opened fire on his supervisor over an unspecified dispute, law enforcement authorities told The Times.

As the supervisor lay wounded, another agent jumped in and tried to subdue the gunman. Another round of gunfire broke out, authorties said.

Officials were investigating whether the gunman turned his weapon on himself, the sources said. The extent of any wounds he may have suffered was not immediately clear.