Slips and surface flooding are causing havoc for motorists in the lower North Island as heavy rain and gale force winds sweep the region.
Police this afternoon urged motorists to drive carefully with dipped headlights after slips on Rimutaka Hill Rd, north of Wellington.
Several hours earlier, a number of small slips closed the Manawatu Gorge, near Palmerston North while a detour via Saddle Rd was partially blocked for a time.
Driving conditions in the Manawatu were "treacherous", New Zealand Transport Agency acting state highways manager David McGonigal said.
"We've got emergency crews working across the network cleaning up slips and managing traffic, but in the meantime we advise motorists to exercise the greatest of care when driving and to avoid unnecessary travel where possible," he said.
Parts of State Highways 1, 3, 54 and 56 were under water.
Further south, roads around Shannon and Levin also flooded as storm water drains struggled to cope with the deluge. Wanganui, Rangitikei and Tararua residents also suffered extensive flooding.
Slips and flooding closed SH3 south of Wanganui, and SH43 in the King Country between Whangamomana and Moki Tunnel.
Wanganui Council infrastructure manager Julian Reweti said consistent rainfall since 5am had pushed the storm water system to its limits.
"More than 100 drainage issues have been reported to council and are being investigated by engineers who will be working until late this evening to assess as many of these as possible," he said.
Five local roads were closed, two of which would remain closed until tomorrow.
Mr Reweti said engineers were also working to fix a power line that "slipped" in Roberts Ave and a broken stormwater pipe.
In the Rangitikei District, Calico Line on SH1, 13km north of Bulls, was closed.
In the northern Wairarapa, the main road between Eketahuna and Pahiatua was closed by flooding.
There were no alternative routes available as local roads were also flooded.
Civil Defence this morning activated its emergency plan for the Hutt River north of Wellington after exceptionally heavy rainfall.
Police said there was concern that the Hutt River might overflow and Block Road at Melling, near the Lower Hutt city centre, had been closed, with the possibility other roads may be affected.
High winds in exposed parts of Wellington and the Wairarapa were expected to ease after they caused havoc on the roads yesterday and today.
An ambulance was blown over while attending a crash in which a van was blown over in severe winds in the Wairarapa yesterday.
The driver of the van and two paramedics suffered minor injuries and were taken to hospital.
A bus was blown off the road near Dannevirke this morning. The driver was the only person aboard, and not injured.
Wind and rain have also caused havoc in the South Island, with heavy rain forecast for Fiordland and the Southern Alps as already swollen rivers and streams threatened to burst their banks.
State Highway 94 between Te Anau and Milford Sound was closed by flooding.