Thousands of people stripped to their underwear and ran through Salt Lake City to protest what they called the "uptight" laws of Utah.

The goal of Saturday's event was to organize people frustrated by the conservative nature of state politics, Undie Run organizer Nate Porter said.

Nudity was prohibited by organizers. Participants donned bras, panties, nightgowns, swimwear or colourful boxer shorts, and some added political messages by expressing support for causes such as gay marriage on their chests, backs or legs.

Salt Lake City is the home of the Mormon church, which is a vocal opponent of gay marriage.

Porter estimated 3,000 people participated in the run, which began in downtown Salt Lake City and circled past the state Capitol building a little over a kilometre away.