Heavy rain has brought a big slip down on to Port Underwood Road in Whatamango Bay in the Marlborough Sounds.
The Marlborough District Council said on Thursday the slip is too dangerous for crews to begin work and it is likely to be several days before it can be cleared.
Specialist geotechnical engineers from Wellington are due to inspect the site on Friday
There is a detour via Rarangi for residents, but it adds an extra 90 minutes' driving for some.
Emergency access is also in place for residents in the Para area, where a bridge has been washed out on Speeds Road, between Blenheim and Picton. The road will stay closed until a temporary bridge can be built.
Meanwhile, contractors were out in force on Thursday working to repair flood-damaged infrastructure including roads and sewerage.
The MetService said 250 millimetres of rain fell in the past few days and, though it has stopped, the flatness of the land meant it would take a while for it to drain.
The council-owned contractor, Marlborough Roads, said workers are prioritising road damage.