The main highway into Wellington is damaged after Cyclone Gita whipped up waves that crashed across the road.
Motorists are already facing heavy delays and southbound traffic into the capital is backed up as far as Raumati.
State Highway 1 was closed between Pukerua Bay and Paekakariki about 12.30am after it sustained weather damage overnight as the high tide washed across both lanes.
The storm surges caused significant damage to guardrails and parts of the footpath on the seaward side of the road collapsed.
Road crews worked throughout the night to clear the debris and the southbound lane heading into Wellington was re-opened shortly after 6.30am.
However motorists were warned to expect "significant delays" and the NZ Transport Agency is urging people to consider delaying trips if possible.
SH1 PAEKAKARIKI TO PUKERUA BAY - ROAD CLOSED - 5:45AM
Due to seawells and debris the road has been CLOSED since 12:30AM this morning. A detour via Paekakariki Hill Road is available for light vehicles however please consider delaying travel through this area if possible. ^IF pic.twitter.com/GFITxmEp1u
Meanwhile two main West Coast routes are cut off this morning.
The road is closed between Jacksons and Kumara and between Haast to Makarora because of strong winds. A number of other main roads around the South Island are also closed after Cyclone Gita, and will be reviewed this morning.
In Canterbury, the Kaikoura Inland Route 70 is closed, plus most of State Highway 1's Kaikoura coast between Hundalee and Clarence. A slip has closed the road between Riwaka and Takaka.
Marlborough/Tasman/Nelson:
• SH60 Riwaka to Takaka – Road closed (slip)
• SH6 Tahunanui to Stepneyville (Rocks Rd, Nelson) – Road open