PCH from Sycamore Road to Las Posas Road will be closed nightly from 6 p.m. to 7 a.m.
Officials say erosion of the oceanside shoulder from high tides and storm damage is to blame.
A Caltrans inspector will check the road conditions every morning to determine when it is safe to reopen.
Caltrans plans to install K-rails to block off the oceanside lane while it begins emergency steps to stabilize the collapsed slope.
Reopening times may vary based on high tides or storm conditions. With more storms expected ahead, drivers should plan alternate routes.