Outrage has intensified across the US as protests, sparked by a grand jury decision not to charge a white police officer for fatally shooting an unarmed black teenager, spread to 170 cities in 37 states.

In Ferguson, Missouri, where 18-year-old Michael Brown was killed by Officer Darren Brown, 2,000 national guard troops were deployed to protect homes and businesses from rioting and looting.

The suburb of St Louis has a predominately black population and a white-dominated police force.

The grand jury’s decision has sparked racially charged protests.

The outrage on the streets now is more intense than the unrest that erupted in the immediate aftermath of the shooting.

Police made 44 arrests and say protesters fired guns and hurled bricks at at them. Several police cars were set alight.