Police officers detain a demonstrator for protesting against the fatal shooting of Michael Brown in Ferguson, Missouri. Photo: Reuters

Police in riot gear ordered lingering demonstrators in Ferguson, Missouri, to disperse late on Tuesday, then charged into the crowd to make arrests as relative calm dissolved in an 11th night of protests over the fatal shooting of a black teenager.

Protests in the town of 21,000, a predominantly African-American suburb of St Louis, have been punctuated by looting, vandalism and clashes between demonstrators and police every night since Michael Brown, an unarmed 18-year-old, was killed by a white police officer on August 9.

Community leaders, politicians and city officials had redoubled their appeals for order on Tuesday, calling for citizens to stay off the streets after sunset, even though a mandatory curfew had been lifted.

In the hours after darkness fell, protesters were notably fewer in number and more subdued than on previous nights. Onlookers milled about as civic activists, members of the clergy and even Missouri Attorney General Chris Koster mingled with demonstrators.

Protests have been punctuated by looting, vandalism and clashes

But as the rally was winding down and most of the protesters were leaving the area, someone among the dozens still in the streets hurled a plastic water bottle at police.

Helmeted officers, some with heavy weapons and dogs, suddenly emerged in force. They ordered the remaining protesters to leave and chased down those who resisted as more bottles were thrown. Several demonstrators were seen being led away in handcuffs, but the number of arrests was not immediately known.

The confrontation capped an otherwise mostly peaceful night of demonstrations, the most tranquil in Ferguson since last Thursday, when a state Highway Patrol captain was placed in command after the local police force was widely criticized for heavy-handed tactics.

The Brown case was due to take a new turn on Wednesday, when the St Louis County prosecutor’s office was expected to begin presenting evidence to a grand jury investigating the shooting. The officer who shot Brown, Darren Wilson, has been placed on leave and went into hiding as Brown’s family and supporters called for his arrest.

US Attorney General Eric Holder was visiting Ferguson, Missouri, hours after nearly 50 protesters were arrested in the 11th straight night of demonstrations over the killing of an unarmed black teenager by a white police officer.

The St Louis County prosecutor’s office will also begin presenting evidence later today to a regularly seated grand jury investigating the August 9 shooting death of 18-year-old Michael Brown.

Prosecuting attorney Bob McCulloch said his office could continue presenting evidence to the grand jury through mid-October as he confronts conflicting pressures for speed and thoroughness.

“On one side, people are saying you’re rushing to justice, and on the other side, they’re saying you’re dragging this thing out,” he said at a news conference. “We’re going to present this as expeditiously as possible, but we are not going to present it in a half-hearted manner.”