Violence has erupted in cities across the US on the sixth night of protests sparked by the death in police custody of African-American George Floyd.

Curfews have been imposed in nearly 40 cities, but people have largely ignored them, leading to tense stand-offs.

Riot police clashed with protesters in New York, Chicago, Philadelphia and Los Angeles, firing tear gas and pepper bullets to try to disperse the crowds.

Police vehicles were set on fire and shops were looted in several cities.

In Minneapolis, where Mr Floyd lost his life, a lorry driver was arrested after reportedly breaching a road barrier before speeding towards a crowd of protesters marching along a major highway.

The National Guard - the US reserve military force for domestic emergencies - said on Sunday that 5,000 of its personnel had been activated in 15 states and Washington, DC, where crowds once again gathered near the White House, this time lighting fires and throwing stones at riot officers.