SAN FRANCISCO (CBS SF) – Hundreds gathered on and around Hippie Hill in San Francisco’s Golden Gate Park Friday, celebrating the first 4/20 day since recreational pot became legal in California.

The unofficial pot holiday started by five friends at a Marin County high school in 1971 and has grown to where festivities were planned worldwide, culminating with a synchronized smoke at 4:20 p.m.

Charles Vance took three weeks to hitch hike to San Francisco from Washington state to take part in the celebration.

“All the people around me,” said Vance for the reason behind his journey. “Sharing the same vibe, the same experience. It’s a communal feeling.”

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The gates opened at 9 a.m. and by noon several hundred people were already at the gathering.

Booths lined the area around the bottom of the hill, selling pot-laced edibles.

San Francisco officials said they expected at least 15,000 people to assemble in time for the 4:20 p.m. smoke. Rec and Park officials estimated that the final crowd size was closer to 20,ooo.

Authorities Friday afternoon confirmed that ambulances were responding to multiple medical emergencies including at least one opioid overdose at Hippie Hill.

As of about 4:30 p.m., no arrests had been reported.

Event producer and Haight Street business owner Alex Aquino said he expected the crowd to exceed the previous years because of it being a Friday, a sunshine-filled day and the legalization of recreational marijuana in the state.

“Last year, we had an incredible turnout and that was on a Thursday,” Aquino said. “Today’s a Friday so it’s getting a lot bigger.”

Aquino said the organizers had doubled security to make sure the vibe stays peaceful and also added a much larger clean-up crew to make sure the park is pristine after the event ends Friday around 6 p.m.

When asked why he thought the crowd would exceed last year, Aquino said legalization will bring more celebrants to the park.

“It’s legal,” he said. “People are partaking and celebrating. On a Friday and beautiful weather and beautiful Golden Gate Park.”

The event also had a strong presence of San Francisco police officers.

“Marijuana is legal, but is illegal to smoke marijuana in public,” Park Station police Capt. Una Bailey said. “The 4/20 event will be inside the

park and within that fenced area people can smoke pot in there. But once they come out onto city streets, no, they will not be allowed to smoke pot. They will be subject to our laws as usual.”

Additionally, Bailey said both uniformed and plainclothes officers would be checking for juveniles smoking marijuana and drivers who may be impaired.

Elsewhere in the Bay Area, there are a wide variety of events planned.

An all-day educational cannabis event is taking place at Oaksterdam University in Oakland, with legal, horticulture and cooking experts on hand, according to Dale Sky Jones of Oaksterdam.

“Our campus is family-friendly. We only distribute knowledge, not cannabis,” Jones said.

The venue is at 1734 Telegraph Ave.

At least two marijuana dispensaries will have extended hours. The Berkeley Patients Group at 2366 San Pablo Ave. in Berkeley will be open until 10 p.m. There will be vendor demos, a photo booth, snacks and raffles all day.

Bay Area Harborside Marijuana Dispensaries will be open until 8 p.m. The dispensaries have two locations, one at 1840 Embarcadero in Oakland, the other at 1365 N. 10th St. in San Jose.