A crumbling cliff forced residents to grab what they could and flee an apartment building atop a Northern California coastal bluff over fears it could slide into the Pacific.

Building officials in Pacifica ordered residents out immediately Thursday morning as large chunks of cliff plunged into the ocean, leaving the 12-unit building just 10 feet from the edge of the wave-battered 50-foot bluff.

The evacuation order was issued after part of the cliff, saturated by recent storms, broke off around 5:30 a.m. Thursday, chief building official Doug Rider said.

An initial evacuation deadline of 5 p.m. was moved up as the cliff continued to crumble. Moving trucks filled the street as about 20 frantic residents packed up what belongings they could.

"It's been insane. I can't even think," said Amanda O'Connell, 24, a swim teacher in this town of 38,000 about 10 miles south of San Francisco.

O'Connell said residents were warned earlier in the week about the deteriorating bluff. She and her boyfriend decided to move some of their larger possessions out early, just in case, she said.

Two nearby buildings also were being monitored but remained stable for the time being, thanks to a wave-deflecting barrier of boulders at the bottom of the bluff, Rider said.

The barrier was erected last spring but did not protect the entire beach. The cliff began crumbling before the barrier could be completed.

The apartment building's owners have received an emergency permit from the California Coastal Commission to put a barrier in place, Rider said. Work is to begin Friday with a crane lifting boulders over the building down to the beach, he said.