Nearly 1,400 people have been arrested across the United States in angry protests that have now spread to at least 30 cities over the death of unarmed black man George Floyd in police custody.

Floyd, 46, died after being arrested in Minneapolis, Minnesota, on Monday.

Police deployed tear gas, flash bombs and batons in an effort to disperse angry protesters who defied curfews imposed by at least 25 cities Saturday night, including Chicago, Atlanta, Los Angeles, Louisville, San Francisco and Denver.

The National Guard was also activated in several states, including Texas, Georgia, Washington, Ohio and Kentucky.

A white policeman was arrested on Friday and charged with third-degree murder and manslaughter.

But the arrest did nothing to quell the protests that began peacefully but later turned violent.

In video footage, Derek Chauvin, 44, can be seen pinning 46-year-old Floyd to the ground with a knee on his neck for more than 8 minutes despite repeated pleas from Floyd that he cannot breathe.

The video went viral online, reigniting public anger over police killings of African Americans, and reopening deep wounds over racial inequality across America.

The case follows the high-profile killings by police of Michael Brown in Ferguson, Eric Garner in New York and others that have driven the Black Lives Matter movement.

Chauvin is due to appear in court on Monday. Three other officers present at the time have also since been fired.

President Donald Trump has put the US Army on alert, saying troops could be deployed on the ground very quickly.

Minnesota remains the most volatile region, with curfews ordered for the Twin Cities of Minneapolis-Saint Paul from 20:00 to 06:00 on Friday and Saturday evening. Protesters defied the curfew.

Trump tweeted Saturday that he had activated the National Guard to do the job that city officials could not do.

Source: Presstv