SANFORD, Fla. - The U.S. man whose fatal shooting of an unarmed black teen led to weeks of national protests before his arrest was released from a Florida jail on $150,000 bail as he awaits trial on a charge of second-degree murder.

George Zimmerman walked out around midnight Sunday, followed a man into a white BMW and drove away. The media shouted no questions at him, and he gave no statement.

His ultimate destination is being kept secret for his safety, and it could be outside the state.

Zimmerman was not charged for more than six weeks in the shooting of 17-year-old Trayvon Martin, sparking national protests led by Martin's parents, civil rights groups and the Revs. Jesse Jackson and Al Sharpton. Martin was black; Zimmerman's father is white and his mother is from Peru.

As with the July 2011 release of Casey Anthony, the Florida woman acquitted of murder in the death of her daughter, Zimmerman was released around midnight. But the similarities end there. Anthony was whisked away by deputy sheriffs armed with semi-automatic rifles as angry protesters jeered. News helicopters briefly tracked her SUV through Orlando before she slipped from public view.

Circuit Judge Kenneth Lester said at a hearing Friday that Zimmerman cannot have any guns and must observe a 7 p.m.-to-6 a.m. curfew. Zimmerman also surrendered his passport.

Zimmerman had to put up 10 per cent, or $15,000, to make bail. His father had indicated he might take out a second mortgage. A website was set up to collect donations for Zimmerman's defence fund. It is unclear how much has been raised.

Bail is not unheard of in second-degree murder cases, and legal experts had predicted it would be granted for the 28-year-old Zimmerman because of his ties to the community, because he turned himself in after he was charged last week, and because he has never been convicted of a serious crime.

Also Monday, the police chief in the city where Martin was shot was to permanently step down from his post under an agreement that still must be approved by city officials.

Sanford Police Chief Bill Lee had temporarily stepped aside as chief March 22 after enduring strong criticism over his department's handling of the case. Police did not initially charge Zimmerman; prosecutors stepped in later.

Martin's parents have a "heavy heart" now that Zimmerman has been released from jail, said Benjamin Crump, an attorney for the 17-year-old's parents, Tracy Martin and Sybrina Fulton.

"They hope his freedom is temporary because the pain he has caused this family is permanent," Crump said Monday.

Zimmerman, a neighbourhood watch volunteer, fatally shot Martin on Feb. 26 inside the gated community where Zimmerman lived. Martin was unarmed and was walking back to the home of his father's fiancee when Zimmerman saw him, called emergency services and began following him. A fight broke out. Investigators say it is unknown who started it.

Zimmerman says Martin attacked him. Zimmerman says he shot Martin in self-defence, citing Florida's "stand your ground" law, which gives broad legal protection to anyone who says they used deadly force because they feared death or great bodily harm.

On Friday, a judge agreed to let Zimmerman out on $150,000 bail. Defence attorney Mark O'Mara has said there are several options for where Zimmerman should go, but would not disclose any of them. Lester on Friday indicated Zimmerman would be allowed to leave the state if arrangements with law enforcement could be made for him to be monitored. He will be fitted with an electronic device.

"The mood in Sanford has calmed down tremendously," said Sanford Commissioner Patty Mahany, whose district includes the neighbourhood where Martin was killed. "I think now that people are able to see the justice system taking place, even though they understand it's going to be quite slow, people are willing to just remain calm and really we're all getting back to our daily routines."

Defence attorneys for other high-profile clients who awaited trial on bail have said Zimmerman should leave Florida and refrain from going out in public.