Transport Agency officials say that on Friday they will reassess whether State Highway 6 will continue to be blocked near Harihari on the West Coast until some time next week.
Earlier they said that it would be at least Saturday before the road could be re-opened, but contractors are warning that it's increasingly likely the road will be closed until after the weekend.
Contractors have struggled to divert water from the flood-swollen Wanganui River where it has scoured out the abutment of the one-lane bridge on the West Coast.
State Highway 6 remains closed after 40 metres of road leading onto the one-lane bridge just north of Harihari was swept away by floodwaters on 2 January.
Nearly 600mm of rain triggered the washout that closed access to Hokitika and Greymouth from much of Westland: there are no simple alternative routes between the West Coast, Wanaka and Queenstown, and drivers are being diverted east of the Southern Alps.
Transport Agency West Coast area manager Mark Pinner says the river has changed direction, which is making it difficult for engineers to assess the bridge's structural integrity.
Heavy rocks are being used to try and force the river back into its original course.
Mr Pinner says the washout may be too large for a temporary bridge, which would mean the road itself would need to be restored.
And Mr Pinner says if the agency feels the bridge isn't safe, a temporary one could be placed over the top of it.
Farmers dump milk
The SH6 closure means that dairy farmers have been forced to dump excess milk because they can't get it to the factory for processing.
Westland Milk Products operations general manager Bernard May said farmers began running out of holding capacity on Thursday morning.
But tankers are being sent from all over the South Island via lengthy detours to try to save some of the excess milk.
Communications company, Chorus said the Wanganui River bridge washout damaged cabling, and it has to run a temporary fibreoptic cable over the river to restore those links.
The outage affected people in Harihari, Haast, Fox Glacier and Franz Josef, and Chorus says a permanent repair will be made over the next few weeks.
Elsewhere on SH6 - from O'Sullivans through Inangahua to Westport - has re-opened after being closed by flooding and slips.
SH69 from Inangahua to Reefton has also re-opened.
But SH65 between O'Sullivans and Springs Junction remains closed following a slip on 2 January and power is out to about 65 houses in the area.
Southland rivers a worry
The Southland Regional Council is warning campers of flooded rivers that could continue to rise.
Up to 50 millimetres of rain fell in the headwaters of the Mataura and Oreti Rivers on Wednesday, and although the rain has eased, they could keep rising as flood waters move downstream from catchment.
The Mataura River at Pyramid Bridge is more than a metre higher than normal and was rising at 52 millimetres an hour on Thursday.
River levels at Gore were predicted to peak in the early hours of Friday.