Three people have been killed and one injured after a cliff collapsed on a popular southern California beach.

Key points: The sandstone cliff gave way in an area popular with locals and tourists

The sandstone cliff gave way in an area popular with locals and tourists Two people were taken to hospital in a critical condition but later died

Two people were taken to hospital in a critical condition but later died Tourists often stand on top of the cliffs for better views of the coastline

The sandstone cliff gave way shortly before 3:00pm on Friday (local time) in Encinitas, a suburb north of San Diego. The area is popular with residents, surfers and tourists.

The beach was filled with people at the time of the collapse. A local news helicopter captured footage of beach chairs, towels, surfboards and beach toys strewn about the sand.

A woman died in the immediate wake of the collapse and two people were flown to hospitals in critical condition. The city announced on Saturday afternoon that both had died.

A fourth person had only minor injures.

Rescue crews were searching for additional victims, but they did not have full access because of safety concerns. Homes on top of the cliff were not in any danger.

Beach cliffs give way four to eight times a year in Southern California, but "nothing of this magnitude", said Brian Ketterer, California State Parks' southern field division chief.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 27 seconds 27 s Aerial footage shows the aftermath of the cliff colapse.

"This is a naturally eroding coastline," Encinitas Lifeguard captain 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 our beaches are actually partially made. It actually has these failures."

The suburbs north of San Diego have contended with rising water levels in the Pacific Ocean, pressuring cliffs along the coast. Some are fortified with concrete walls to prevent multi-million-dollar homes from falling into the sea.

Tourists often stand on top of the cliffs for better views.

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.

Some areas are only accessible by steep wooden stairs that descend from neighbourhoods atop the cliffs.

Emergency responders and a search team work at the scene of the cliff collapse. ( Reuters: Mike Blake )

AP