Cliff Owen/AP Photo

Alyssa Newcomb, Olivia Katrandjian and Matt Larotonda contributed reporting.

Occupy D.C. protesters say things turned violent today when U.S. Park Police clad in riot gear and on horseback raided their camp to enforce a ban on camping in McPherson Square, a national park.

At least seven protesters were arrested. Officials said the situation became tense when an officer was struck in the face with a brick, The Associated Press reported.  The officer was taken to a hospital for treatment.

The raid, which started around 5:30 a.m., stretched into the late afternoon as police sectioned the camp off using barricades and cleared each quadrant individually.

"It's been a hell of a day so far. We were pushed out of the park violently by the police. The police formed two parallel lines and began squashing protesters into each other. Once police realized their mistake, that they had essentially given us no way out, they began hitting people to get them out of the park. The ground is wet and muddy, and so it's very dangerous. Many people were hurt. A number of people have to see medics for their injuries," Justin Jacoby Smith, a member of the media team of Occupy DC, told ABCNews.com.

Many tents have been carried away in a garbage truck, leaving large swaths of the park vacant.

"They effectively removed any kind of bedding from the tents and they're going to start searching them soon," Legba Carrefour, a spokesman for Occupy D.C. told ABCNews.com.  "We're still watching this unfold. The cops are still here in force."

Protesters have been fearful of a final confrontation with authorities since last week, when the National Park Service announced the camping ban.

"This is not an eviction," Sgt. David Schlosser, a spokesman for the National Park Service Police said in a statement.

Regulations in the federal park permit protesters to stay around the clock and have tents on the premises, however they are barred from sleeping.

The NPS regulations also called for the removal of a large tarp that had been placed over a statue of Civil War Gen. James McPherson. Dubbed the "Tent of Dreams," the makeshift shelter was also removed today.

Four people were arrested for stepping over police barricades and refusing to leave the base of the statue.

"The tarp is a symbol," a camp inhabitant said. "It's emblematic of our quest for freedom for people all around the world. This isn't just about economic freedom here in the US."

A handful of Occupy D.C. members have gone on a no-sleep strike to protest the rule.

"People are focusing on saving their personal possessions. The plan is to regroup and then we are going to escalate," Carrefour said. "Occupying isn't limited to parks and squares."

City officials, including Washington Mayor Vincent Gray, have expressed concern over the sanitary conditions of long-term encampment.

During the raid inspectors in yellow hazmat suits worked their way through the park removing some tents and camping aids such as sleeping bags.

Some demonstrators told ABC News that a contingent of more hard-line park inhabitants had left bags of human waste as boobytraps hidden throughout the area.

The D.C. encampment is one of the few camps still standing after the Occupy Wall Street movement began in New York City's Zuccotti Park on Sept. 17.