More thunderstorms are expected for the region after torrential rain damaged numerous sections of State Highway 6 south of Hokitika on Saturday. The highway remains closed between Haast and Harihari on Sunday.
The small south Westland township on the western bank of the Whataroa River was now cut off by slips and washouts on all roads leading in and out.
The New Zealand Transport Agency said it would be several days before access was cleared.
The owner of the backpacker hostel and campground, Madeleine Dennehy, spoke to RNZ on the phone from Whataroa, while very loud thunder rolled in the background.
She said a touring cyclist and some freedom campers were now sheltering from the storm at her hostel.
"They were pretty shook when they came here at 4am. They'd started waking each other up and saying they'd better move as the back tyres of one of them (vehicles) was in the river, basically.
"They told me they'd parked up right above the [Whataroa] river where they were meant to have parked."
She said five campervans had arrived at the backpacker hostel, and she was concerned if others might have been stranded.
"It happened two nights previously that someone had to be towed out at 2am.
"There are flooding signs there but people don't understand what happens to our rivers here, that they just go nuts."
Ms Dennehy said she had tried heading to the river two nights ago to check, but the thunder and lightning was so bad and the rain so heavy, she could not get out of her driveway.
"Everyone got up to milk yesterday but there was no power, but everyone still has to milk the cows, but now the tankers can't get through."
She said currently the hostel was not in any immediate danger, but water did go through the back of the building and shifted an empty freezer.
The downpours last night were not as severe as the night before, she said, and the 1kg Milo tin she used to collect rain leaking through the ceiling had not filled up today, as it had last night.
"I did have to upgrade it, from a smaller tin I had there."
Ms Dennehy was running low on some essential supplies, and regretted not stocking up on potatoes as she had planned last week.
"We've got a lot of food in the freezer so we're good there but toilet paper supplies are running low."
4WD TRACK CUT FOR EMERGENCIES ONLY
Civil Defence said a four-wheel-drive track had been cut north of Harihari but only emergency service vehicles, milk tankers and local residents were allowed to use it.
The road from Haast to Makarora would open at 10am, but only one lane.
The NZ Transport Agency said the worst damaged parts - between Franz Josef and Fox Glacier - were unlikely to be reopened for days.
Mayor of Westland Bruce Smith said there was no sign yet of the heavy rain letting up.
Further north, Mayor of Grey District Tania Gibson said they had escaped the worst of the weather and there were no reports of damage in that area of the coast.
Westpower said power was still down between Fox Glacier and Paringa, and could be out for a day or two.
