Protesters clashed with police in Anaheim, California on Tuesday during the fourth night of demonstrations following the shooting death of an unarmed man.

Police fired pepper-spray projectiles and rubber bullets after some 500 people had gathered at city hall. Shop windows were smashed by some protesters and there were 24 arrests, police said.

Manuel Angel Diaz was shot dead by police on Saturday afternoon in Anaheim. Officers have admitted Diaz was not carrying a gun when he was killed.

The violence broke out after protesters demonstrated outside a meeting at city hall to discuss Diaz's shooting. Police prevented people from attending the meeting when it became too crowded, before issuing a dispersal order at about 9pm.

NBClosangeles.com reportedreported that "within minutes" protesters were fleeing the area as police fired pepper balls at the crowd. Police also used batons to clear protesters, some of whom threw objects and chanted at the police, according to reports.

Fires broke out as the evening progressed, while officers with shotguns guarded shops after protesters smashed the windows of at least six stores. A witness told Reuters that protesters had thrown chairs through the windows of a Starbucks.

Anaheim police spokesman Sergeant Bob Dunn said 20 adults and four minors were arrested. He said a police officer, two members of the media and some protesters were injured, but no one was taken to hospital.

One man who was in the crowd, Geoffrey Giraffe, wrote on Twitter that a man had been shot in the head by a rubber bullet while retreating from police. He posted a picture which showed a man bleeding from a cut to the back of his head.

An Anaheim resident who lives close to where the protests took place told the Guardian she could hear sirens and helicopters all afternoon and into the night.

"I was very concerned, since I live near and shop in the shopping center which had broken windows," said the woman, who did not want to be named. She said she was forced to stay in as "many of the major streets near my house were blocked off", however she added that the protests "seemed to be disorganised".

Police say Diaz, 25, had fled from officers who approached him as he stood by a car in an alley with two other men. Police said he was a known gang member but have admitted he was not carrying a gun when he was killed. Video footage showed officers standing over his body.

Residents have accused police of racial profiling, and Diaz's mother, Genevieve Huizar, filed a civil rights and wrongful death lawsuit against the city and the police department on Tuesday. The suit alleges that the unarmed Diaz was shot execution-style with a bullet to the back of the head after he had already been hit in the leg, the Los Angeles Times reported.

Another man, Joel Mathew Acevedo, was shot and killed after he fired at an officer on Sunday night, police said. The police union has issued a statement defending the officers involved in the shootings. It said both men killed were gang members who had criminal records. FBI spokeswoman Laura Eimiller said the agency is conducting a review to determine whether a civil rights investigation is warranted.

Diaz and Acevedo's deaths bring to five the number of people killed by police shootings in Anaheim this year. There have been eight shootings in the city this year involving the police, according to officials.