By Fiona Ortiz

FERGUSON Mo. (Reuters) - Hundreds of people demonstrated in the pouring rain in the St. Louis area on Monday, staging a series of rolling protests in the latest show of anger over the police killing of an unarmed black teenager in August.

Several demonstrators were arrested in protests at the Ferguson Police Department where protesters sang "We Shall Overcome," an anthem of the civil rights movement of half a century ago, and others chanted: "No justice, no peace."

Protesters also attempted to shut down a street in front of Emerson Electric in St. Louis, holding signs reading: "Black lives matter," and other slogans. Some demonstrators tried to block a major intersection in Ferguson, while others gathered to demonstrate at Soldiers Memorial Park, and some marched on St. Louis City Hall, where they tried to hang a banner reading: "Which side are you on?"

At least 19 people were arrested by St. Louis County police by early afternoon, according to St. Louis County spokesman Brian Schellman.

Several other events were scheduled through the day, said Mervyn Marcano, a spokesman for "FergusonOctober," the four days of protests culminating on what organizers call "Moral Monday."

Local and national clergy, civil rights groups, activists and community organizers were helping lead the demonstrations, which they said were aimed at drawing attention to what they say is police mistreatment of blacks, and building momentum for a national movement against police violence.

"This is a historic day," said Marcano.

Many traveled from across the United States to join in the protests. One of those arrested on Monday at the police department was activist, author and academic Cornel West.

Numerous protests have been held in the two months since the Aug. 9 killing of Michael Brown, 18, by white police officer Darren Wilson. Tensions escalated after a white officer in St. Louis shot and killed another 18-year-old black man, Vonderrit Myers Jr., last Wednesday.

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A grand jury is considering charges against Wilson, who has been placed on administrative leave. Protesters want Wilson arrested immediately and have called for the appointment of a special prosecutor. The U.S. Justice Department has launched a civil rights investigation into Brown's death.

"The weekend has been incredible to help re-energize those of us that are here," said Ferguson Democratic Committeewoman Patricia Bynes. "The message is getting out there."

Although the demonstrations have largely pitted black protesters against white police officers, people of many races and backgrounds participated in the protests.

"I believe in my black brothers and sisters and the fact they feel they are threatened by the police and that racial profiling is going on," said Brenden Graczak, a 22-year-old white man from St. Louis who joined the demonstration at the police department.

More than 1,000 protesters shouted slogans at police on Sunday night into Monday in St. Louis, near where the white off-duty officer shot and killed Myers. Police said Myers had opened fire, but his family said he was unarmed.

(Reporting by Fiona Ortiz and Kenny Bahr in Ferguson, Missouri; Additional reporting and writing by Carey Gillam in Kansas City, Mo.; Editing by Jim Loney, Will Dunham and Peter Cooney)