SH6 between Belgrove to Kohatu will remain closed until at least Friday afternoon.
The main route between Nelson and Murchison closed on Thursday after rockfall came down onto the road.
The road will be assessed again late on Friday afternoon as to whether it can reopen.
A detour is in place, which is suitable for all vehicle types, and road users are advised to plan accordingly and to allow extra time for the detour.
The detour takes travellers along Wai-iti Valley, Stock, Valley and North Rds, beofre coming back onto SH6.
