Arizona secret forest party of 5,000 people busted by police

US Forest Service workers broke up a party of more than 5,000 people that had been organised in the Tanto National Forest near Chandler, Arizona.

Law enforcement officials in the Sycamore Creek area on Saturday night discovered the huge gathering, according to the US Forest Service.

Local news station KPHO-TV said partygoers tried to restrict access to parts of the park by taping sections off.

Susan Blake, a spokeswoman for the Tonto National Forest, said it was likely the largest unauthorised gathering the park has ever experienced.

Any group with more than 75 participants has to fill out an application to gather in the park.

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"There were, you know, DUIs. There were plenty of tickets issued for riding two up on ATVs. Not wearing helmets for children," Ms Blake said.

Other violations racked up by party goers includes speeding, reckless vehicle operation, camping in illegal areas, blocking roadways, target shooting and illegal use of fireworks.

Photos from the event that circulated on social media showed large crowds of people waving glowsticks and watching performers on a makeshift stage.

Officers said there were several vehicle accidents reported associated with the party and that they received multiple stolen vehicle reports. In one instance, an individual had to be life-flighted out and hospitalised after a pair of four-wheelers collided.

Officers said the party appeared to have been organised on Facebook groups aimed at off-road enthusiasts.

The off-roading group that organised the party said its members spent the next day cleaning up the mess made by the party. Their garbage was not the top concern of law enforcement officers responding to the scene.

According to the US Forest Service, the party put the "public, Forest Service personnel, and first responders at risk".

Officials with the Maricopa County Sheriff's Office said there have not been any arrests made in relation to the party and that it did not know who was ultimately responsible for the party.

Sandy Bahr, who represents the Grand Canyon Chapter of the Sierra Club, an organisation dedicated to conservation, particularly of the western US wilderness, lamented at the likely damage the party goers did to the park.

"Well, I was horrified to see it," Ms Bahr said. "That many people engaged in those types of activities in one area – it's going to be super destructive."

Tanto National Forest is the seventh-largest national forest in the US, spanning more than 2.9 million acres.