A growing chorus of celebrities, including former US President Barack Obama, have called for justice for George Floyd, the African-American man who was killed in police custody in Minneapolis on Monday, EDNews.net reports citing ABC News.

In a tweet, Obama said for millions of Americans, being treated differently on account of race was the norm.

The US is reeling from the aftermath of the death, which was filmed by a passer-by and has sparked protests and riots in several states.

The full Minnesota National Guard has been activated for the first time since World War II after days of peaceful protests and destructive riots.

Governors in several other states also called in National Guard troops as protests over repeated police killings of black people grew on Saturday from New York to Tulsa to Los Angeles, where police fired rubber bullets to scatter crowds and at least one police car burned.

On Friday, the officer who held his knee to Floyd's neck was arrested and charged with third-degree murder and second-degree manslaughter — but protesters are calling for the other three officers to be arrested.

Former First Lady Michelle Obama also joined the fray, saying she was "exhausted by the heartbreak that never seemed to stop".

Meanwhile, President Donald Trump has been criticised for promoting violence after tweeting that the rioters who looted Minneapolis stores should be shot dead.

"These THUGS are dishonouring the memory of George Floyd, and I won't let that happen. Just spoke to Governor Tim Walz and told him that the Military is with him all the way. Any difficulty and we will assume control but, when the looting starts, the shooting starts. Thank you!"

In response, Twitter hid Trump's tweet, saying it violated the social network's rules about glorifying violence, though it was still viewable behind the notice.

Television personality Oprah Winfrey tweeted a statement saying that George Floyd's name would not become just a hashtag, but will be a cry for justice.

Actor Jamie Foxx spoke to a local television channel saying it was hard for a black man to raise his children in the current environment and that "we are not afraid to stand".