Michael Brown shooting: Driver smashes into crowd as protests erupt across the US during a second night of unrest

Protests erupted in cities across the United States during a second night of demonstrations following a grand jury's decision not to indict a white police officer who shot dead unarmed black teenager Michael Brown.

As more than 2,000 National Guard troops were deployed in a bid to prevent rioting and looting in the St Louis area, demonstrations against the decision taken in Ferguson, Missouri, swelled from Los Angeles to Washington.

Shocking scenes were seen at a rally in Minneapolis when a car smashed into a crowd of protesters before appearing to trap one woman under the front left wheel.

The woman, who suffered minor injuries during the incident, was one of several hundred who had gathered near the 3rd Precinct police outpost to show solidarity with Brown.

The driver is reported to have called police soon after to inform them of the incident. Police spokesman John Elder said the incident was under investigation.

President Barack Obama has appealed for a dialogue in the wake of the grand jury decision, while his attorney general promised a federal probe into the shooting would be timely and rigorous.

Officer Darren Wilson, the policeman who shot the teenager, said his conscience was clear.

Brown's death on 9 August led to days of violent clashes between police and protesters in the immediate aftermath - tensions which have since flared again in the wake of the decision.

In Ferguson, despite the increased military presence, a police car was set on fire near City Hall as darkness fell, while officers fired smoke bombs and tear gas to scatter protesters.

While a total of 44 arrests were made, the unrest was said to be less intense than on Monday night in the immediate aftermath of the grand jury decision.

In Los Angeles, protesters flooded the US 101 freeway, carrying barricades that were then laid across lanes, bringing traffic to a standstill.

The few dozen protesters, who were soon chased off the highway and corralled on an overpass, had broken away from a larger, primarily peaceful group of hundreds who had marched for miles through the city, converging on police headquarters.

Police cars and businesses were vandalised meanwhile in Oakland, where two major freeways were also briefly shut by protesters.

In Cleveland, where 12-year-old Tamir Rice was shot dead by an officer on Saturday while carrying a pellet gun, several hundred protesters marched down a freeway ramp to block rush-hour traffic.

"The system wasn't made to protect us," said one of the protesters, 17-year-old Naesha Pierce. "To get justice, the people themselves have to be justice."

In New York, police used pepper spray after protesters tried to block the Lincoln Tunnel and Triborough Bridge and marched to Times Square.

Protesters also blocked traffic in Atlanta, while in Boston a march took place past a correctional facility where inmates taped Mr Brown's name on a window in solidarity with demonstrators.

Peaceful demonstrators marched in Seattle and Albuquerque while rallies also formed in Michigan, Maine, Wisconsin and other states.

Several hundred from colleges in Georgia held peaceful demonstrations. As the night wore on however, some groups split off and tried to block a freeway.

Police said 21 people were arrested, mostly for failure to disperse when asked, but one person faces a weapons charge.

Roughly 1,000 people meanwhile attended a rally in Portland, Oregon, before marching through downtown.

A group of about 300 continued to march into east Portland. Traffic was disrupted with police making several arrests.

Additional reporting by Reuters and AP