FERGUSON police officer Darren Wilson, who had been on administrative leave since he shot dead 18-year-old Michael Brown on August 9, resigned from the police on Saturday.

Mr Wilson, who had been with the Ferguson Police Department for less than three years, said he decided to step down after the department told him it had received threats of violence if he remained on the force.

"I'm not willing to let someone else get hurt because of me," he said.

But protesters upset by a grand jury's decision not to indict the police officer were unmoved by his resignation and indicated that it would not affect their search for justice.

Activists disrupted shopping in outer St Louis for a second straight day.

Demonstrators marched through a Trader Joe's store in Brentwood, about 10 miles south of Ferguson, on Saturday.

After leaving they briefly blocked a road near a motorway.

On Friday, three St Louis-area shopping centres had been briefly shut down due to demonstrations.

More than 100 protesters gathered near the Ferguson police headquarters on Saturday night following the news.

At least one person was arrested after a brief standoff with officers.

Many of the protesters seemed unconcerned about the resignation. Several merely shrugged their shoulders when asked what they thought.

And equality campaigner Rev Al Sharpton, who preached at a church service attended by Mr Brown's parents today, said: "We were not after Darren Wilson's job. We were after Michael Brown's justice."

Following last Monday's announcement that the grand jury would not indict the white officer, a dozen commercial buildings were destroyed in Ferguson and neighbouring Dellwood, not far from where Mr Brown was killed.

By Tuesday, Missouri governor Jay Nixon had sent more than 2,200 National Guard troops to Ferguson to support police.

Though protests calmed significantly, more than 100 people have been arrested since then, including 16 at a protest outside police offices.

Elsewhere, police in Portland, Oregon, said 10 people were arrested on Saturday night "after a large group of protesters lay down in the street."