MINNEAPOLIS (REUTERS) - Americans anxiously awaiting a verdict in the trial of Derek Chauvin reacted with jubilation and relief on Tuesday after a jury found the former Minneapolis police officer guilty of murdering George Floyd during an arrest last May.

But elation over the trial's outcome, capping nearly a year of social upheaval, racial tensions and political strife stoked by Floyd's killing, was tempered by calls for a continued fight against inequalities pervading the United States criminal justice system.

In George Floyd Square, the traffic intersection named after the 46-year-old Black man who died with his neck pinned to the street under Chauvin's knee, throngs of people screamed, cheered and applauded at the news of the guilty verdict.

The square has become a place of pilgrimage and protest since Mr Floyd's death made him the face of a national movement against racial injustice and police brutality. Protests against his killing swept the United States and the world last year in the midst of the coronavirus pandemic.

"It's not Chauvin on trial. It's America on trial," Ms Marcia Howard, one of the volunteers who oversees barricades and tributes in the square, said tearfully.

Floyd's dying words, "I can't breathe," were recalled in street demonstrations against his killing that convulsed the US and the world last year in the midst of the coronavirus pandemic.

"I can breathe," said Ms Lynea Bellfield, a 43-year-old Black woman who joined a festive celebration in the square. "It feels like the beginning of something special. I had to bring my grandsons to see it."

A brass band played in a nearby church parking lot in the sunshine and people snacked on baked goods donated by well-wishers, smiled and took pictures. Chants of "George Floyd" went up every so often.

A 12-member jury found Chauvin, 45, guilty of all three charges against him - second- and third-degree murder and manslaughter - after deliberating for just over 10 hours in a trial that encompassed three weeks of testimony from 45 witnesses. Chauvin was quickly led away from the courtroom in handcuffs after the verdict was read.

Meanwhile, a federal civil rights investigation into Mr Floyd's death is ongoing, US Attorney General Merrick Garland said in a statement following Chauvin's conviction.

The trial outcome brought cheering people to the streets and motorists honking their horns in a number of major US cities, including Washington and New York City, according to social media.

In Brooklyn, a crowd gathered outside Barclays Center to celebrate. Mr Robert Bolden waved an American flag as he embraced Ms Ingrid Noel, who wore camouflage. A child wearing a red mask rode on an adult's shoulders, while others prayed.

The announcement also brought elation to crowds gathered outside the Hennepin County courthouse where the trial was held.

Tears rolled down the face of Mr Chris Dixon, a 41-year-old Black Minneapolis resident, as he took the verdict in.

"I was hoping that we would get justice, and it looks like we did," said Mr Dixon, a director of athletic diversity and inclusion at Augsburg University. "I'm just very proud of where I live right now."

"As a country we don't have a history of holding police accountable. And when you are a Black man, that's difficult to deal with and swallow every day," Mr Dixon said.

The verdict brought new hope, he said. "Not just Black people, but folks of all different races and cultures just said this was unacceptable."

For many, the sense of joy was blunted, however, by the tragedy of Floyd's death and awareness that racial inequality remains deeply rooted in American society.

Protesters outside the courthouse called for a continued focus on the prosecution of another Minnesota police officer, Kimberly Potter, charged with manslaughter after shooting a young Black motorist, Daunte Wright, during a traffic stop on April 11 miles away in the suburb of Brooklyn Centre.

"Indict, convict, send those killer cops to jail. The whole damn system is guilty as hell," protesters chanted.

Some took over the main thoroughfare in front of the courthouse, blocking traffic.

Officials in Brooklyn Centre, embroiled in several nights of clashes between protesters and police following Mr Wright's death, set an 11 pm curfew for Tuesday.

"The change is coming, so watch out," Mr Floyd's girlfriend Courtney Ross, told MSNBC.

Early reaction was also somber in Floyd's hometown of Houston, where a childhood friend, Mr Travis Cains, said it was crucial that Chauvin be sentenced to the full extent of the law.

"African Americans just want to be treated as humans. That's all we're asking for - is that too much?" Mr Cains told Reuters.

"We're tired of all this police brutality that been going on for years, we're tired of these public lynchings."

Law enforcement and public safety officials in Minnesota and elsewhere had braced for the possibility of an outpouring of rage had the jury acquitted Chauvin or deadlocked in a mistrial.

Citing the "threat of civil unrest," Minnesota Governor Tim Walz on Monday had declared a preemptive state of emergency for the Minneapolis metropolitan area and requested security assistance from other states.

Many businesses in Chicago boarded up their windows in anticipation of possible disturbances.

And Florida Governor Ron DeSantis on Monday signed an "anti-riot" bill into law, imposing tougher penalties for people found to have engaged in violent protests. He noted then his expectation of potential fallout from a Chauvin trial verdict.

Here are some reactions to the verdict, seen as a milestone in the fraught racial history of the US and a rebuke of law enforcement's treatment of Black Americans:

US President Joe Biden: " 'I can't breathe.' Those were George Floyd's last words. We cannot let them die with him. We have to keep hearing them. We must not turn away. We cannot turn away. This can be a moment of significant change."

Former US President Barack Obama and Michelle Obama: "Today, a jury did the right thing. But true justice requires much more. Michelle and I send our prayers to the Floyd family, and we stand with all those who are committed to guaranteeing every American the full measure of justice that George and so many others have been denied."

Ms Hillary Clinton, Former US Secretary of State and Democratic presidential candidate: "George Floyd's family and community deserved for his killer to be held accountable. Today, they got that accountability. Always and forever, Black lives matter."

Minnesota Governor Tim Walz: "Today's verdict is an important step forward for justice in Minnesota. The trial is over, but our work has only begun. The world watched on May 25, 2020 as George Floyd died with a knee on his neck for nearly nine minutes. Thousands of Minnesotans marched in the streets last summer in the wake of his death - inspiring a movement around the globe. While many of these people never met George, they valued his humanity. They knew what happened was wrong. They called for change, and they demanded justice."

UK Prime Minister Boris Johnson: "I was appalled by the death of George Floyd and welcome this verdict. My thoughts tonight are with George Floyd's family and friends."

American Civil Liberties Union: "For the first time in Minnesota state history, a white police officer has been held accountable for killing a Black man. While today's verdict is a small win for police accountability and may help heal a grieving community, the systems that allowed George to be murdered - ripping him away from his family and the communities that loved him so much - remain fully intact."

National Association for the Advancement of Coloured People: "Justice has prevailed in the case against #GeorgeFloyds killer #DerekChauvin, but the work is not done! We must keep fighting to end qualified immunity, and we must get #PoliceReformNOW."

US Senator Raphael Warnock: " My heart goes out to the Floyd family. Thankfully today they received something that approaches justice. Obviously, it will not bring George Floyd back. Hopefully this is the beginning of a turning point in our country, where people who have seen this trauma over and over again, will know that we have equal protection under the law."

Ms Alexandria Ocasio-Cortez, US Representative: "That a family had to lose a son, brother and father; that a teenage girl had to film and post a murder, that millions across the country had to organise and march just for George Floyd to be seen and valued is not justice. And this verdict is not a substitute for policy change."

National Fraternal Order of Police: "The trial was fair and due process was served. We hope and expect that all of our fellow citizens will respect the rule of law and remain peaceful tonight and in the days to come."

Mr Adam Silver, National Basketball Association Commissioner, and Ms Michele Roberts, Executive Director of the National Basketball Players Association: "George Floyd's murder was a flash point for how we look at race and justice in our country, and we are pleased that justice appears to have been served. But we also recognise that there is much work to be done and the National Basketball Association and the National Basketball Players Association, together with our newly-formed Social Justice Coalition, will redouble our efforts to advocate for meaningful change in the areas of criminal justice and policing."

Maryland Governor Larry Hogan: "The senseless murder of George Floyd served as yet another reminder that we still have a long way to go to live up to our nation's highest ideals. Justice has now been served, and we hope that this verdict will bring some measure of peace to the Floyd family and the community."