The three personnel are safe and accounted for following the partial collapse of the Santa Cruz Wharf, officials said.
The collapse occurred at 12:45 p.m. PT on Monday "as the result of very strong waves crashing into it," Santa Cruz Mayor Fred Keeley said during a press briefing.
Two of the people who went into the water were rescued, while the third swam to safety, he said.
"We believe that everyone that went into the water is now accounted for and safe," Keeley said.
No members of the public were on the wharf, which has been closed to the public, at the time it collapsed, officials said.
The wharf will remain closed until further notice and its structural integrity is being assessed, officials said.
The municipal wharf has been undergoing a $4 million restoration following storm impacts, according to Tony Elliot, the director of Parks and Recreation for the city of Santa Cruz.
About 150 feet at the end of the wharf collapsed, including a restroom and a part of the renovation, he said. Equipment from the construction also went into the water, he said.
A city project manager and two contracted engineers who were monitoring the wharf when it collapsed went into the water, officials said. No serious injuries were reported, officials said.
People are advised to stay away from the area, as well as the shorelines, due to debris in the water and a high surf advisory.
The National Weather Service in the Bay Area warned that "dangerous and life-threatening beach conditions" are forecast for beaches along the Pacific Coast through Tuesday, including rough seas and breaking waves up to 60 feet.
The Santa Cruz County Sheriff's Office issued an evacuation order Monday afternoon for oceanfront residents along an approximately 3-mile stretch of shoreline just south of Santa Cruz, citing large swells and high tides.