At least three people were wounded on Saturday when shots were fired at a massive rally of marijuana smokers in Denver, in the western state of Colorado, city police said.
Shots rang out in the crowd around 5:00 pm (2300 GMT) at the rally of several thousand people gathered at the city's Civic Center Park.
The crowd had massed in the park to celebrate April 20, marked in the United States as 4/20 -- a reference to 420, a code term referring to marijuana use.
Voters in Colorado and Washington last November approved proposals to legalize the possession of small quantities of marijuana by individuals in their respective states. However federal law still considers marijuana an illegal drug.
"1 male & 1 female shot. Both victims shot in leg & suffered non life-threatening inj," Denver police wrote in a Twitter message.
Police later said that a third shooting victim, described as a juvenile who was grazed by bullet, walked into a city hospital.
Local TV showed a chaotic breakup of the gathering after the shots were fired, and a panicked rush to leave the area that surprisingly left no other victims.
Police are searching for two suspects believed to have fired the shots.
Laura Forduno, who was at the rally, told the Denver Post newspaper that the rally "was peaceful. Everybody was having fun and then you heard the shots -- pow-pow-pow-pow -- and everybody started to run."
Event organizer Miguel Lopez told the newspaper that all events scheduled for the rest of the day and for Sunday were canceled.
Many Americans are still in shock after the bombings Monday at the Boston Marathon that killed three people and wounded 140.
Earlier this month, a Pew Research Center opinion poll indicated that for the first time in more than four decades of polling on the issue, a majority of Americans -- 52 percent -- think marijuana should be legalized.