A 30-foot-long slab of the cliff plunged onto the sand near Grandview Beach north of San Diego. A KNSD-TV helicopter captured footage of beach chairs, towels, surf boards and beach toys strewn about the sand.
Other beachgoers and lifeguards at a nearby tower scrambled to the towering pile of debris, which was estimated to weigh tens of thousands of pounds, to help dig out victims.
"I saw first responders, and I saw lifeguards frantically digging people out of the debris," Jim Pepperdine, who lives nearby, told the San Diego Union-Tribune.
Pepperdine said he saw people trying to resuscitate a woman before her body was covered.
A woman died at the scene, and two more people later died at hospitals. Another person was taken to a hospital, and a person who had minor injuries was treated at the scene, according to statements from the city.
Their names and ages were not immediately released. All the victims were adults, authorities said.
Search dogs were brought in to hunt for other possible victims, and a skip loader was brought in to move the dense, heavy debris. No other victims were found by late Friday night.
The beach is reached by wooden stairs from a parking lot above. Homes atop the cliff were not in any danger, Encinitas Fire Chief Mike Stein said.
The cliff remained unstable and complicated the search effort, Stein said.
Suburbs north of San Diego have contended with rising water levels in the Pacific Ocean, pressuring bluffs along the coast. Some bluffs are fortified with concrete walls to prevent multimillion-dollar homes from falling into the sea.
Long stretches of beach in Encinitas are narrow strips of sand between stiff waves and towering rock walls. People lounging on beach chairs or blankets are sometimes surprised as waves roll past them and within a few feet of the walls.
Grandview Beach is fairly narrow, with tides high this week. Surfers lay their boards upright against the bluff.
Cliffside collapses are not unusual as the ocean chews away at the base of the sandstone, authorities said. Some beach areas were marked with signs warning of slide dangers.
Several people have been killed or injured over the years in bluff collapses. The Tribune reported that Rebecca Kowalczyk, 30, of Encinitas died near the same area on Jan. 16, 2000, when a 110-yard-wide chunk of bluff fell and buried her.
Bluffs give way four to eight times a year in Southern California, but "nothing of this magnitude," said Brian Ketterer, southern field division chief of California State Parks.
"This is a naturally eroding coastline," Encinitas Lifeguard Capt. Larry Giles said. "There's really no rhyme or reason, but that's what it does naturally. .... This is what it does, and this is how are beaches are actually partially made. It actually has these failures."