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The Department of Conservation has called in engineers and has not yet given a timeframe for reopening the road, which gives tourists viewing access of the glacier.
The road was washed out at the same place during ex-tropical Cyclone Fehi on February 1, when 350m of the causeway was swept away.
It took almost two months to repair at a cost of about $1million.
Doc said yesterday heavy rain at the weekend had activated a large landslip in the Fox Glacier Valley, causing the Fox River from the bottom of the glacier to overtop the road.
South Westland operations manager Wayne Costello said yesterday morning valley access was restricted as a result.
"Vehicles and walkers cannot get access, but scenic flights are still operating.''
Franz Josef Glacier, to the north, remained open to vehicle and foot access.
Mr Costello said Lake Matheson, well-known for its mirror-like reflections of the Southern Alps on calm days, was a great alternative walk for visitors to Fox Glacier.
"At this time, we are unsure how long access to the valley will be restricted. We are currently assessing options and would need to wait until it is safe and practical to do work, if that is feasible.
"We will be seeking the advice of geotechnical and civil engineers when looking at options for remediation work.''
The West Coast Regional Council does not record rainfall at Fox Glacier, but nearby Franz Josef received 138mm over the weekend, most of that falling on Saturday.