Several witnesses said they saw one shooter.
The park, which sits on a hill, was crowded with people, including children in a playground and running around the grass.
Juhasz said she saw two people who had been shot.
San Francisco police advised people to stay away from Dolores Park right after the shooting but lifted that advisory two hours later. "I was yelling at people, 'It's actually a gun, it's actually a gun'".
According to the SFPD, the three victims - identified Friday as a 37-year-old man, a 16-year-old male, and a 69-year-old man - were located "near the vicinity of the foot bridge at Church and Cumberland Streets".
"I normally can handle (myself) well in these situations, but I was pretty sure I had just lost my life", he said, the Chronicle reported.
Other witnesses said the men then scattered into the neighborhood. Later, authorities said two of the victims, both males, were in critical condition.
Police say three people were shot and transported to hospitals but didn't release other details.
Several witnesses stated that about half a dozen men, some wearing bandanas to hide their faces, started shouting and acting threateningly on a bridge that leads into the park. 3 shooting victims at this time.
"At first people didn't totally react because it sounded like fireworks", said Juhasz, a writer and freelance journalist.
Juhasz said the police responded quickly to the incident.
"We need more police presence in the park because there are all sorts of shady characters and non-park-like activity when you think of a family park", Lopezjones added.
No suspect is in custody, and the area is under investigation as an active crime scene; police are asking drivers to avoid the area and are setting up a command post nearby.