State Highway 1 north and south of Kaikoura is unlikely to reopen to traffic until at least mid next week, a week after Cyclone Gita, the New Zealand Transport Agency says.
Multiple road and rail sites are blocked with rocks and soil.
NZTA says the likely reopening date for one lane of traffic will be reviewed next Monday.
Large slips and rockfalls are blocking State Highway 1 near Kaikoura, while the West Coast was also hit.
Around 300,000 cubic metres of material needs to be cleared from 60 sites both north and south of the town, from Parnassus on the south side, to Clarence on the north, NZTA Earthquake Recovery Manager Tim Crow said in an update this evening.
The biggest of these is just south of Okiwi Bay at Jacob's Ladder, north of Kaikoura, and is around 200,000 cubic metres alone, he said.
Two debris flow bridge areas under construction north of Kaikoura in Half Moon Bay, south of Ohau Point, took a significant hit from large amounts of material pouring off the hills, sluiced off by the record downpour, Mr Crow said.
"Much of this material is sitting on steep hillsides and gullies, loosened by the earthquake, and will continue to pour off the hills whenever there is significant rain - which this was."
One debris flow bridge area has already been cleared by crews working since yesterday morning in Half Moon Bay.
More than 200 mm of rain fell in 24 hours, and at Rosy Morn, south of Kaikoura, more than 300 mm.
Around 5000 cubic metres of material washed down the hill at Rosy Morn with two nearby houses, not inhabited the night of the storm, filled with debris.
"Once we reopen, there will be several more single lane sections of highway while the road is restored to pre-storm condition as soon as possible," Mr Crow said.
"People will need to factor in some additional time for this journey for several weeks until we get all the material removed and back to our rebuild and resilience work."
While State Highway 1 is closed people can get to Kaikoura via the inland road (Route 70) via Waiau and Mt Lyford.
Drivers travelling between Picton and Christchurch need to take the Lewis Pass Route via Murchison and St Arnaud.
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