Gunfire has erupted at a Colorado park during a massive annual marijuana celebration, injuring two people and sending tens of thousands fleeing, police said.
A crowd that had been expected to swell to 80,000 had gathered at the Denver park to mark the counter-culture holiday known as 4/20 - the first celebration since Colorado and Washington made pot legal for recreational use.
The shooting happened shortly after people shared hugs and joints in a mass 4.20pm smoke-out.
Police spokesman Sonny Jackson confirmed two people had been shot and both were taken to a hospital with injuries that did not appear to be life-threatening.
Witnesses said they heard three or more shots. Aerial footage showed the crowd frantically running from the park.
A seizable police force on motorcycles and horses had been watching the celebration. But officers did not arrest people for smoking in public, which is still illegal.
Ian Bay, who was skateboarding through the park when the shots erupted, said he was listening to music on his headphones when he looked to his right and saw a swarm of hundreds of people running at him. "I sort of panicked. I thought I was going through an anxiety thing because so many people were coming after me," he said.
Authorities generally look the other way at public pot smoking in the park on April 20. Police said before the event they were focused on crowd security after Monday's attacks that killed three near the finish line of the Boston Marathon.
Nationwide, group smoke-outs had been planned on Saturday from New York to San Francisco. The origins of the number "4/20" as a code for pot are murky, but the drug's users have for decades marked the date 4/20 as a day to use pot together.
Colorado and Washington are still waiting for a federal response to the votes on legalising marijuana and are working on setting up commercial pot sales, which are still limited to people with certain medical conditions. In the meantime, pot users are free to share and use the drug in small amounts.