Mayor Rahm Emanuel said Wednesday that Chicago police must be better trained to distinguish between when they can use a gun and when they should use a gun, after a series of shootings by officers sparked protests that police are too quick to fire their weapons.

Emanuel announced changes in police training and department policies on use of force during a news conference. He also said the police department will double the number of Tasers available to officers — to 1,400 from 700 — as he works to restore public trust in the police force and his administration.

"Our police officers have a very difficult and dangerous job. They put their lives on the line so the rest of us can be safe. And like all of us, they are human and they make mistakes," the mayor said. "Our job is to reduce the chances of mistakes.

"That requires us to give them the right guidance, the right training, and the right culture, to prevent abuses," he said. "Willful misconduct and abuse cannot and will not be tolerated."

Emanuel pledged training to make police encounters with citizens "less confrontational and more conversational." He said "force should be the last option and not the first choice."

Every police patrol car will be equipped with a Taser, an electroshock weapon designed to disable a person, by June 1, 2016, he said.

Quintonio LeGrier

Quintonio LeGrier, 19, threatened his father with a bat before he was shot and killed by a Chicago police officer. (Handout)

Interim police supt. John Escalante said the city looked at 15 police departments, including New York, Seattle, Cincinnati and Cleveland as it developed its policy changes.

Emanuel and Chicago police have been under heavy scrutiny since the city, under court order, released a squad car video last month showing white officer Jason Van Dyke shooting  Laquan McDonald 16 times in 2014. The black youth, 17,, armed with a knife, is seen veering away from Van Dyke in the video before the veteran officer starts firing.

Van Dyke, who faces six first-degree murder counts, pleaded not guilty to the charges Tuesday.

The release of the video set off weeks of demonstrations, forced the resignation of police Supt. Garry McCarthy and has led to a wide-ranging civil rights investigation of the entire Chicago Police Department by the U.S. Department of Justice. Protesters also have called for Emanuel to resign.

Activists were skeptical Wednesday that the changes would reverse decades of problems and mistrust between Chicago residents and police.

Ted Pearson, one of the leaders of the Chicago Alliance Against Racist and Political Repression, noted that Emanuel made leadership changes after the release of the McDonald video and gave a speech before the city council in which he apologized, appearing at times to be near tears.

Yet that didn't stop a shooting last weekend, in which police killed two people:Bettie Jones, 55, who police said was shot accidentally, and Quintonio LeGrier, 19.

Elsewhere, more protests were planned in Cleveland on Wednesday, two days after a grand jury decided not to charge two white police officers in the 2014 shooting death of Tamir Rice, a black 12-year-old boy who was playing in a park with a toy gun that shoots plastic pellets.

Cleveland officials said on Tuesday they will review Rice's shooting to determine whether the officers involved or others should face disciplinary action.

Tensions over race and policing in Chicago and Cleveland come amid intense scrutiny of police killings in the United States over the past 18 months, especially of black men. Protests have taken place around the country.

About 1,860 officers — or roughly 15 per cent of Chicago's police force — have completed the the department's crisis-intervention team training, according to department statistics. Advocates for the program say that number should be 25 to 35 per cent.

In saying the number of Tasers will be doubled, Emanuel mentioned the McDonald shooting. He noted that on audio recordings of communications between dispatchers and officers on the scene that night, several officers can be heard "frantically" asking for a Taser before the shooting.

Police have said no officers or vehicles on the scene were equipped with one.

"There's a problem that has to be addressed," Emanuel said.