The Irish rock band U2 has cancelled its Saturday night concert in St. Louis after police told concert organisers that they couldn't provide a typical level of security because of protests.

Hundreds marched on Friday after a judge acquitted a white former St. Louis police officer in the 2011 shooting death of a black suspect.

Police say nine city police officers and one State Highway Patrol officer were injured in Friday's protests, reports News.com.au.

There were 23 arrests before 6pm local time and an unknown number of additional arrests after that.

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The band says on its website that it can't in good conscience risk its fans' safety. The site outlines plans for refunds.

Hundreds marched for hours in mostly peaceful demonstrations on Friday, until a broken window at the mayor's home and escalating tensions led riot-gear-clad officers to lob tear gas to disperse the crowds.

Activists had for weeks threatened civil disobedience if Jason Stockley were not convicted in the 2011 death of 24-year-old Anthony Lamar Smith.

Hundreds marched on Friday after a judge acquitted a white former St. Louis police officer in the 2011 shooting death of a black suspect. Photo / Getty
Hundreds marched on Friday after a judge acquitted a white former St. Louis police officer in the 2011 shooting death of a black suspect. Photo / Getty

That stirred fears of civil unrest and the erecting of barricades around police headquarters, the courthouse where the trial was held and other potential protest sites.

More than 20 arrests were made by early on Friday evening. Police reported that 10 officers had suffered injuries by the end of the night.