An FBI investigation is underway as four officers have been fired after a white officer pinned his knee against the unarmed 46-year-old black man named George Floyd's neck as he struggled to breathe.

According to Minneapolis police, the encounter between Floyd and officers occurred right after 8 p.m. Monday, when police were called to the 3700 block of Chicago Avenue South on a report of a man attempting to use forged documents at Cup Foods. The store manager declined to comment on the issue.

Officers found Floyd in a car at the scene. He appeared to be influenced as police officers ordered him to get out of the car, he "physically resisted", according to the statement.

"After he got out, he physically resisted officers," police spokesman John Elder told reporters early Tuesday. "Officers were able to get the suspect into handcuffs and officers noticed that the man was going into medical distress."

Overnight, video of the attempted arrest circulated on social media. The video was posted by Darnella Frazier on Facebook. It shows the nine-minute video of a white officer pressing his knee into Floyd's neck behind a car. While lying face down on the road, Floyd repeatedly groans and says he can't breathe.

"Please, man, I can't breathe," he says.

Floyd repeats the phrase again and again: "I cannot breathe. I cannot breathe."

"He's not even resisting arrest right now, bro," one bystander tells the white officer and his partner, in the video. "You're f-ing stopping his breathing right now, you think that's cool?"

After about five minutes, Floyd stops moving and appears unconscious. People in the gathering crowd started shouting, pleading for the officers to check Floyd's pulse. The officer does not lift his knee until medical personnel arrive and carry him to an ambulance.

CBS News obtained video of Floyd's initial arrest, and it seems to contradict the claim that he resisted the police, at least in the early stages of their encounter.

The police department said an investigation was underway. The Minnesota Bureau of Criminal Apprehension and FBI would be included, police noted without elaboration.

"He should not have died," Mayor Frey said Tuesday. "What we saw was horrible, completely and utterly messed up. ... Whatever the investigation reveals, it does not change the simple truth that he should be with us this morning."

"Being Black in America should not be a death sentence," Frey continued. "When you hear someone calling for help, you are supposed to help. This officer failed in the most basic human sense."

Meanwhile, social media users noted similarities between Floyd's death and that of Eric Garner, an unarmed Black man who died in 2014 after being placed in a chokehold by a New York City police officer.

Just like Floyd, Garner repeatedly said, "I can't breathe" before he died.