George Zimmerman, charged with second-degree murder in the killing of unarmed black teenager Trayvon Martin, left a Florida jail early on Monday after posting bail of $150,000 in the racially charged case, a spokeswoman for the sheriff in Seminole County, Florida, said.

Zimmerman, a former neighbourhood watch volunteer, was released from the county's John E. Polk Correctional Facility shortly after midnight Monday after posting bail and meeting other conditions set for his release at a pretrial detention hearing on Friday.

Under the conditions set by Judge Kenneth Lester Jr., Zimmerman must wear an electronic monitoring device, although he may be allowed to leave the state. He must also observe a dusk-to-dawn curfew and is prohibited from consuming illegal drugs or alcohol or possessing a firearm.

No date has been set for Zimmerman's trial but, due to safety concerns, his whereabouts are expected to remain a closely guarded secret until his next appearance in court.

Zimmerman shot and killed Martin is a gated community in Sanford in central Florida on February 26 in an incident that triggered civil rights protests nationwide and fired a national debate over guns, self-defence laws and race in America.

Zimmerman, who is white and Hispanic, has said he shot the 17-year-old Martin in self-defence following a confrontation that occurred as Martin was returning to his father's house in the community after buying candy from a convenience store.

Police initially declined to arrest Zimmerman, citing Florida's Stand Your Ground law, which allows people to use deadly force when they believe they are in danger of getting killed or suffering great bodily harm.

The lack of an arrest led thousands to march in protest rallies in Sanford and across the country. The public outrage forced the Sanford police chief and regularly assigned prosecutor to step aside.

At the Friday hearing, Zimmerman apologized to Martin's family, stunning a rapt courtroom after he appeared in a suit and tie and with shackles around his waist and wrists.

Governor Rick Scott appointed Angela Corey as special prosecutor. She charged Zimmerman on April 11.

(Reporting by Greg McCune and Tom Brown; Editing by Philip Barbara)