Protests continued for a sixth day across the U.S. over the death of unarmed black man George Floyd at the hands of a police officer in Minneapolis, Minnesota. In total, more than 20 states and about 40 cities imposed curfews for Sunday.

Meanwhile, a serious divide has emerged among Donald Trump's top allies and advisers over how the president should address the rallies and riots. 

Democratic presidential candidate Joe Biden on Sunday toured the site of one of the protests that ripped through U.S. cities overnight and called for protesters against police brutality not to turn to violence.

Biden, wearing a face mask, made his second appearance outside his Delaware home since the coronavirus crisis hit in March.

"Protesting such brutality is right and necessary," Biden said in a statement emailed shortly after midnight. "But burning down communities and needless destruction is not."

Meanwhile, the president poured fuel on an already combustible situation with more violent rhetoric, such as "when the looting starts the shooting starts" and "if they had they would have been greeted with the most vicious dogs, and most ominous weapons."

Biden will face Trump in the November 3 presidential election. Trump's re-election campaign manager, Brad Parscale, said on Saturday that Biden should deliver a more forceful condemnation of violence.

A new ABC News/Washington Post poll shows Biden clearly ahead of Trump. Biden's up by a 53-percent to 43-percent margin among registered voters in the survey.

According to CNN, there were more than 40 national public polls taken at least partially in the month of May that asked about the Biden-Trump match-up. Biden led in every single one of them. 

Trump is being urged by some advisers to formally address the nation and call for calm, while others have said he should condemn the rioting and looting more forcefully or risk losing middle-of-the-road voters in November, CNN reported.

Congresswoman Ilhan Omar ripped Trump on Sunday over his conduct throughout the protests, condemning the president for his incendiary comments. 

"This president has failed in really understanding the kind of pain and anguish many of his citizens are feeling," said Omar. 

Omar's district remains the center of national protests since the arrest that led to Floyd's death took place in Minneapolis. 

Keisha Lance Bottoms, mayor of Atlanta, the hometown of Martin Luther King Jr., called for people to channel their anger and sorrow into something "more meaningful and effective through non-violent activism" and saying the president "is making it worse" and is stoking racial tensions.

"He should just stop talking. This is like Charlottesville all over again," Bottoms told CNN's Jake Tapper on "State of the Union." "He speaks and he makes it worse. There are times when you should just be quiet and I wish that he would just be quiet." 

Bottoms is under consideration to be presumptive Democratic presidential nominee Joe Biden's running mate.

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Dan Eberhart, a Republican donor and supporter of Trump, said the president, with election looming in five months, is focused on catering to his core supporters rather than the nation at large. "Trump is far more divisive than past presidents," Eberhart said. "His strength is stirring up his base, not calming the waters."

Robert O'Brien, the president's national security adviser, said the president would continue "to take a strong stand for law and order" even as he understood the anger over Floyd's death.

While some aides urged Trump to keep off Twitter as they mapped out a more considered strategy, Trump could not resist blasting out a string of messages on Sunday once again berating Democrats for not being tough enough and attributing the turmoil to radical leftists.

"Get tough Democrat Mayors and Governors," he wrote. Referring to Biden, he added: "These people are ANARCHISTS. Call in our National Guard NOW. The World is watching and laughing at you and Sleepy Joe. Is this what America wants? NO!!!"

As politicians in the U.S. scramble to deal with the new situation, protests nationwide continue and move to other cities across the world, with thousands joining protests against Floyd's death, shouting "No justice! No peace!"