LeBron James and other high-profile athletes have taken to social media to voice their outrage over the death of a black Minnesota man who was pinned down by police.

George Floyd, 46, died Monday night while in Minneapolis police custody. A bystander's video showed an officer kneeling on the handcuffed Floyd's neck, even after he pleaded that he could not breathe and stopped moving.

James weighed in Tuesday night on Instagram with a post referencing Colin Kaepernick, the former NFL quarterback who famously kneeled during the national anthem to protest police brutality and racial injustice.

James' post includes a photo of the officer kneeling on Floyd's neck alongside a photo of Kaepernick kneeling during the anthem, topped with the caption: "This ... ... Is Why." The Los Angeles Lakers star wrote in the post: "Do you understand NOW!!??!!?? Or is it still blurred to you?? #StayWoke"

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Do you understand NOW!!??!!?? Or is it still blurred to you?? ??‍♂️ #StayWoke?

A post shared by LeBron James (@kingjames) on May 26, 2020 at 4:38pm PDT

James has been outspoken on social issues like police brutality throughout his career. He also posted an Instagram story Tuesday that included a photo and video of Floyd's arrest along with the caption: "We're hunted."

Former NBA player Stephen Jackson was friends with Floyd and has shared a number of social media posts about his death. Jackson, who currently works as an ESPN analyst, called Floyd by the nickname "Twin" and noted that "both of our names will live forever."

NFL stars Odell Beckham Jr. and DeMarcus Lawrence, NBA stars Jaylen Brown and Donovan Mitchell, and WNBA Hall of Famer Lisa Leslie also tweeted their frustration over Floyd's death.

Worlds honestly sickening. It really is..... no explanation

— Odell Beckham Jr (@obj) May 27, 2020

DONE BEING QUIET AND DONE BEING ANGRY. HOW CAN WE FEEL SAFE WHEN THOSE MEANT TO PROTECT US ARE KILLIN' US?!!!! WHEN WILL MINORITIES BE FREE TO BE AMERICANS IN AMERICA!?

— DeMarcus Lawrence (@TankLawrence) May 26, 2020

If I was in attendance I would have been arrested for sure https://t.co/odtTz8cKhg

— Jaylen Brown (@FCHWPO) May 27, 2020

SICKENING!!! I HAVE NO WORDS MAN!!! https://t.co/vrFJAcRw55

— Donovan Mitchell (@spidadmitchell) May 27, 2020

If anybody that follows me is not outraged about these senseless attacks on BLACK MEN, please stop following me! If your spirit is not disturbed, please stop following me! This inflicted Pain but it will never inflict FEAR... sorry, were not made like that! #BlackMenMatter pic.twitter.com/A9tSSzOSh6

— Lisa Leslie (@LisaLeslie) May 27, 2020

Kaepernick also shared a version of the photo on his Instagram stories that had been tweeted by former NFL wide receiver Nathan Palmer. Formula One star Lewis Hamilton shared James' post on his Instagram stories as well.

Four Minneapolis officers involved in Floyd's arrest were fired Tuesday after the video of the incident gained national attention. Mayor Jacob Frey announced the firings on Twitter, saying "This is the right call."

Floyd's death was under investigation by the FBI and state law enforcement authorities. It immediately drew comparisons to the case of Eric Garner, an unarmed black man who died in 2014 in New York after he was placed in a chokehold by police and pleaded for his life, saying he could not breathe.

Protesters filled the intersection Tuesday night in the street where Floyd was arrested. They eventually marched about 2½ miles to a city police precinct, with some protesters damaging windows and a squad car and spraying graffiti on the building.

The Associated Press contributed to this report.