DENVER – As many as police officers – including at least one on a bicycle – were hit by a car while he was monitoring traffic near a student protest.

Students had walked out of school to protest the Ferguson, Missouri grand jury decision involving police officer Darren Wilson.

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A witness tells CBS 4 one of the officers was dragged about a block.

Students left class this morning at about 10 am and disrupted traffic. Cars could be seen backed up while kids blocked the intersection.

The group of an estimated 1,000 people walked through downtown Denver, around the Capitol building, by city and county buildings and eventually to the 16th Street Mall.

It was then the officer was assisting the crowd to get back to East High School when he was hit.

The Colorado Springs Gazette reports “four mangled bicycles” could be seen at the location.

A nurse on the scene was covered in blood, and a wide area was cordoned off by police, according to the paper.

The department tweeted about the incident:

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About three dozen police vehicles, ambulances and fire trucks were on the scene.

UPDATE: The Denver Channel reports the officer is in “extremely critical condition.”