Former US president Barack Obama says the nationwide protests following the death of George Floyd in police custody have provided the opportunity for people to be "awakened" and "change America".

"In some ways, as tragic as these past few weeks have been, as difficult and scary and uncertain as they've been, they've also been an incredible opportunity for people to be awakened to some of these underlying trends," Mr Obama said.

Mr Obama's speech offered a contrast in tone to the way his successor, Republican President Donald Trump, has responded to the protests, some of which have devolved into violence.

Mr Obama said this mobilisation of young people was sparking a change in mindset across the country.

"That's a direct result of the activities and organising and mobilisation and engagement of so many young people across the country, who put themselves out on the line to make a difference," he said.