Caerphilly County Borough Council has implemented an emergency road closure of the B4251 Newport Road between Gelligroes and Ynysddu as a result of a landslip.
Diversions are available via the A472, A467 and the local road network.
The road will be closed for the entire weekend.
A Caerphilly County Borough Council spokesman said: “Engineers will continue to monitor the situation and open the road as soon as it is safe to do so.
“Diversionary routes will be installed today, which are via the A472, A467 and the local road network.
“CCBC apologises for any inconvenience this may cause.”