Authorities in Castro Valley on Wednesday closed Redwood Road after a large portion of the roadway collapsed.
The road closure, which is located at mile marker 7.38, blocks all access between Castro Valley and Oakland, officials said.
All motorists and pedestrians are being advised to stay away from the area.
Those wishing to navigate to Lake Chabot campground facilities are required to enter the site from the Oakland side of Redwood Road, according to authorities.
Engineers are working on a repair plan. Crews said the road has been failing for a while and finally gave way Wednesday.
No estimated time when the road will reopen.