CHICAGO (Reuters) - Hundreds of protesters marched through the streets of Chicago and staged “die-ins” on Thursday, calling for the resignation of embattled Mayor Rahm Emanuel a day after he emotionally apologized for the 2014 police shooting of a 17-year-old black teen.

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The day’s protests started with dozens of medical students of different races lying down in front of City Hall for 16 minutes at the start of the work day, some holding signs reading “Do No Harm” in a demonstration broadcast by local media.

The protesters chose 16 minutes to symbolize the 16 times white police officer Jason Van Dyke shot Laquan McDonald in 2014.

Release of police video of the shooting and the filing of a murder charge against Van Dyke on Nov. 24 came more than a year after McDonald’s death, and the delay, which activists blame on Emanuel and the top local prosecutor, has prompted more than two weeks of protests in the nation’s third-largest city.

Another demonstration unfolded during evening rush hour in the city’s downtown.

About 500 people marched from City Hall to Millennium Park, at times stopping traffic and making sharp, unexpected turns that forced police to scramble to catch up. The march was one of the largest in Chicago since the release of the video.

Protesters held signs demanding the resignation of Emanuel and Cook County State Attorney Anita Alvarez and for an overhaul of Chicago’s police board. At times, they chanted “16 and a coverup!”

Dane Tucker, a retired Chicago firefighter who believes Emanuel should step down, brought his 10-year-old grandson to the protest.

“At some point we all have to get together and say, ‘enough is enough,’” Tucker said. “We have to be as one, that’s the only way we can fix this.”

High-profile killings of black men by law enforcement in U.S. cities have stirred a national debate about the use of force by police, particularly against racial minorities.

Emanuel has recently taken steps to reform the police department, including setting up a task force to review police accountability and firing the police superintendent.

But outrage has mounted over the McDonald shooting and police misconduct overall. Two black state representatives have introduced a bill that would allow the mayor to be recalled.

“We can’t continue to have a city that’s in turmoil like this,” said Representative La Shawn Ford, who like Emanuel is a Democrat and sponsored the bill. Ford told Reuters the bill, which would not be considered until mid-January, would allow the community to prove their rhetoric is serious.

Meanwhile, the city began a nationwide search for a new police superintendent. The Chicago Police Board, a group of citizens appointed by the mayor, is taking applications through Jan. 15, it said.