State Highway 94 closed at 4.30pm on Monday and Tuesday due to heavy snowfall and crews have worked to clear the road.
It reopened at 9am today, but road users were advised to drive with care.
The road will close again at 4.30pm today due to heavy, warm rain forecast overnight, which can trigger avalanches.
A spokesman for Waka Kotahi/Milford Road said rain on recent new snow from the last few weeks has raised the avalanche hazard to high.
More heavy rain was expected for Thursday and the Milford Road may remain closed. The avalanche risk would extend into Friday.
"More storms are forecast in the coming week that will also affect the highway access to Milford Sound," he said, as part of spring conditions.
MetService has issued a heavy rain warning for Fiordland from 3am until 7pm on Thursday, with between 80mm and 1100mm of rain, mainly about the ranges. Peak rates of 10mm/h to 20 mm/h were expected in the morning.
Heavy rain may cause streams and rivers to rise rapidly. Surface flooding and slips are also possible and driving conditions may be hazardous.
A strong wind watch was also in place for Fiordland from midnight tonight until noon on Thursday. Northwest winds may approach severe gale in exposed places.
Meanwhile, severe gales were likely for Southland, Clutha and Stewart Island from midnight until noon on Thursday, and for the Canterbury High Country from 8am until 8pm on Thursday, with northwesterlies gusting to 120km/h in exposed places.
- ODT Online
