Newly released recordings of 911 calls made when a Florida neighbourhood-watch captain shot and killed an unarmed African-American teenager are fuelling community outrage and allegations of police bias.

George Zimmerman, 28, claims he shot 17-year-old Trayvon Martin in self-defence, believing a suspicious teen was roaming around his Sanford, Fla. neighbourhood.

On the night of Feb. 26, Martin was returning to his father's gated community, where he had been watching the NBA All-Stars game on TV. He had dashed to a nearby convenience store during a break in the game and was only holding a bag of Skittles candy and a bottle of iced tea when he was shot.

"This guy looks like he's up to no good or he's on drugs or something," Zimmerman is heard telling the dispatcher in one of the 911 recordings just released by police. "He's got something in his hands. I don't know what his deal is."

"These a*******, they always get away," he says.

"Are you following him?" the dispatcher asks Zimmerman at one point during the call.

"Yeah," Zimmerman replies.

"OK, we don't need you to do that, OK?" the dispatcher says.

But shortly afterward, a shot was fired, prompting frantic 911 calls from neighbours.

"He just said he shot him," one of the residents can be heard telling the dispatcher. "Yes, the person is dead lying on the grass. Oh my God."

Martin's parents and local residents are outraged that police have not laid any charges against Zimmerman. They allege police either botched the investigation or turned a blind eye because the teen is black and the shooter is white.

In a letter to a Florida newspaper, Zimmerman's father said his son has received death threats and moved out of his home. The father also said Zimmerman is Hispanic and grew up in a multiracial family.

"He would be the last to discriminate for any reason whatsoever ...," the letter said. "The media portrayal of George as a racist could not be further from the truth."

Critics also question why police did not look into Zimmerman's criminal record while investigating the shooting. He has been arrested before for assaulting a police officer.

With files from The Associated Press