Police arrested four people at the site of Occupy Denver, including two charged with arson for allegedly setting the makeshift shelters on fire as officers moved in just before midnight.

Two other people were arrested for failing to obey a police officer's order, KUSA reports.

Some of the protesters took a knee in Tim Tebow-style as the police began clearing the area near the Civic Center shortly before midnight, The Denver Post reports. The crowd of around 40 then sang God Bless America before retreating.

Police Chief Robert White said officers had hoped to convince demonstrators to remove their belongings on their own, but moved in after two protesters began setting fire to the shelters, The Post says.

A firetruck then moved in to quickly douse the flames.

"We certainly respect their First Amendment rights and it wasn't our intention to infringe on those rights," White said in impromptu remarks to reporters, The Post reports. "But also value the rights of other citizens who live in our community."