A section of the highway between Murchison and O'Sullivan's Bridge had reopened by Sunday evening after a slip was cleared.
"The road is open to two lanes, but under a 30km/h temporary speed limit," Waka Kotahi said.
"Drivers must drive with care through the slip site.
"The temporary speed limit will change to 50km/h on Tuesday at 7.30am, when work at the road's shoulder will be carried out at the site."
State Highway 6 was still closed from the bridge to Inangahua due to another slip in the Buller Gorge, Waka Kotahi said.
It would remain closed overnight.
"People travelling between Nelson and Westport must avoid the area or delay their travel until this section of State Highway 6 reopens," Waka Kotahi said.
All other roads affected by Saturday's bad weather had since reopened.
The flooding and snow also stranded motorists. Two people had to be rescued in Marlborough after driving into flood waters near Spring Creek on Saturday night.
A bus carrying 26 passengers also slid off the road on its way to Mt Cook Village on Saturday afternoon.
There were no injuries but the bus could not be towed and alternative transport was arranged for the passengers.
Police said the bus was driven onto a closed road in snowy conditions.
The case had been referred to WorkSafe's commercial vehicle safety team.
Most snow restrictions have now been lifted.
Queenstown Lakes District Council said this morning that crews had cleared snow from Crown Range Rd overnight and there were no chain requirements today.
"However, please drive to the conditions as they could change at any time."
In Dunedin, some surface flooding occurred, closing Old Brighton Rd.
