The United States Justice Department says it's investigating the fatal police shooting of a black man whose death was caught on camera.

Bystanders used mobile phones to capture the moment 37-year-old Alton Sterling was killed outside a convenience store in Baton Rouge, Louisiana on Tuesday.

The footage appears to show two white police officers wrestling Mr Sterling to the ground before shooting him at point blank range.

The incident has sparked civil rights protests on the streets of Louisiana, with demonstrators chanting "black lives matter".