Several cities across the U.S. have been besieged by crowds who defied curfews to protest the death of an unarmed black man, George Floyd, in the hands of a Minneapolis police officer, Derek Chauvin.

In a viral video shot by a bystander, Mr Floyd, 46, was about a week ago seen handcuffed, his neck pinned to the ground by Mr Chauvin, his nose bleeding, as he gasped for breath.

“Please, I can’t breathe,” Mr Floyd groaned.

The police accused him of forgery.

Another video shot at a different angle showed that three policemen kneeled on Mr Floyd, according to local media CNN, while another officer stood to restrain bystanders from the scene.

Minutes later, Mr Floyd laid motionless, his eyes shut, as his head dangled against the pavement. He was declared dead at a hospital shortly afterwards, CNN reported.

All four officers have been fired, according to the police. Police also said Derek Chauvin had been arrested and charged with third-degree murder and second-degree manslaughter.

But protesters and critics believe the charges are not harsh enough. Angst has since spiked across the country as thousands poured onto streets in demonstrations, some peaceful, others ending in chaos.

The U.S. is also the epicenter of COVID-19 with over a million cases and 100,000 deaths, but this appeared to be the least worries of the demonstrators who went on the solidarity march.

Some protesters were seen in videos launching fireworks and throwing bottles at police barricades. Others torched buildings, burned police cars and even looted stores, CNN said.

In Minneapolis, the city where the incident occurred, a police station was set ablaze, and parts of the city experienced looting and vandalism. Dozens of arrests have been made, but no serious injuries were recorded, the Minnesota department of corrections commissioner Paul Schnell said.

In downtown Indianapolis, Police Chief Randal Taylor said at a press conference Saturday night that at least three people were reported shot and one dead amid the protests.

At least 27 people were arrested in protests Saturday night in Seattle, Washington, according to Seattle Police Department chief Carmen Best.

Also, a 27-second video posted on microblogging site Twitter showed a New York police truck drive into a barricade, and plowing through protestors who were seen throwing objects at the vehicle.

It was unclear if there were injuries or casualties, but New York City Mayor Bill de Blasio told reporters Saturday the police were investigating and maintained that the police might have been left with no choice.

“Look, I’ve seen that video, and I’ve obviously heard about a number of other instances — it’s inappropriate for protestors to surround a police vehicle and threaten police officers,” CNN quoted Mr De Blasio as saying.

“And so it’s clear that a different element has come into play here who are trying to hurt police officers and trying to damage their vehicles, and if a police officer is [in] that situation they have to get out that situation.”

An officer in Jacksonville, Florida, was “stabbed or slashed in the neck and is currently in the hospital,” state police officer Sheriff Mike Williams told a press conference Saturday.

Elsewhere, police responded with rubber bullets, tear gas, pepper spray and arrests, including of reporters. Local reports say 25 cities in 16 states have imposed curfews. Some states have called in the National Guard soldiers to help quell the unrest. California has declared a state of emergency.

In a statement by Democratic Party presidential hopeful Joe Biden, he said “protesting such brutality is right and necessary.”

“It’s an utterly American response,” Mr Biden wrote. “But burning down communities and needless destruction is not. Violence that endangers lives is not. Violence that guts and shutters businesses that serve the community is not.”

President Donald Trump has been criticised for his comments about the protesters, calling them thugs and threatening to deploy the military to quell the protests.