The St. Louis area on Thursday was bracing for more racial unrest over the August killing of unarmed black teenager Michael Brown by a white police officer, and another police killing of a black teenager on Wednesday was expected to add fuel to the fire.
Several civil rights organisations and protest groups, including Hands Up United, planned to mark the weekend with marches and rallies in St. Louis and the suburb of Ferguson, Missouri, where Brown was killed two months ago.
The groups are demanding the arrest of the officer who killed Brown, and want to draw attention to police treatment of black Americans. Protest organizers said they are planning only peaceful activities, but fear that Wednesday's killing of the black teen in the south St. Louis neighborhood of Shaw might trigger violent outbursts.
"We never advocate violence ... But I do know that people were angry last night and they will be out this weekend," said Tory Russell, a leader of Hands Up United. "I don't know what they are going to do."
At least 6,000 have registered on an organising website for the "weekend of resistance" events in and around Ferguson, which kick off on Friday with a "justice now" march to the office of St. Louis County Prosecutor Bob McCulloch. The weekend is to be capped with actions of "civil disobedience" on Monday.
Organizers said they are also planning to create a "memory altar" to victims of police violence and to hold a candlelight march carrying a coffin to the Ferguson Police Department.
The Hands Up United Web page shows posts from people looking to share rides to St. Louis from Los Angeles, Milwaukee, Dallas, Boston and New York.
Ferguson Mayor James Knowles said law enforcement officers throughout the area are planning for large crowds and possible violence.
"There are a lot of people coming into town," said Knowles. "We are going to be prepared. There is intel out there that there are people wanting to do bad things. And people who want to cause a problem are going to use that (the shooting on Wednesday) as a rallying cry," he said.
In the Shaw incident, a 32-year-old white St. Louis police officer fatally shot 18-year-old Vonderrit Myers Jr. after the officer, who was off duty working for a private security company, saw Myers and two friends running and pursued them, according to a statement issued by the St. Louis police department.
Myers pulled a gun and shot at the officer and then the officer fired several shots, fatally wounding Myers, police said.
The police department would not identify the officer, but said he was not hurt and has been placed on administrative leave as the shooting is investigated.
Relatives of Myers said he did not have a gun, the St. Louis Post-Dispatch reported.
The shooting sparked protests that raged until dawn on Thursday. One person was arrested and three police vehicles were damaged in the unrest, police officials said.
The Myers killing comes as the St. Louis area is still struggling with unrest after the Aug. 9 killing of Brown by Ferguson police officer Darren Wilson. Brown was unarmed when he was shot at least six times.
"There is a real breakdown of trust in law enforcement," said Rashad Robinson, executive director Color of Change, a national online civil rights organisation helping to promote the protests. "But people are trying to build momentum for reforms that need to happen in communities around the country."