By Krystal Gibbens and Tess Brunton of RNZ
MetService is warning people to prepare for gales and heavy rains, which are already battering parts of Canterbury, the West Coast, Otago, Southland and Wellington.
The weather has already triggered multiple callouts for fire crews. At least seven flights have been cancelled - five Dunedin flights and two Invercargill flights - due to high winds, while some ferries have also been cancelled.
With the weather expected to ramp up, MetService are warning most of the country will be hit with a "fairly volatile" week of weather.
The Transport Agency is also warning drivers to drive to conditions ahead of possible 130km/h gusts across the Wellington, Wairarapa and Tararua districts on Monday evening.
NZTA said drivers should expect hazards such as sudden gusts, wind-blown debris, fallen trees and downed powerlines.
It said extra care would be needed on exposed routes, such as State Highway 2 Remutaka Hill and State Highway 1 Transmission Gully - Wainui Saddle.
State Highway 2 on the Remutaka Hill may have to close, NZTA said.
Orange strong wind and heavy rain warnings are already in place for much of the South Island, while an Orange Strong Wind Warning for Wellington will come into effect at 10pm, and would go through to 6pm on Tuesday.
MetService has recently added a heavy rain watch for Southern Lakes, Mackenzie Basin and parts of the Canterbury High Country from 9am on Monday, and a strong wind watch for Christchurch and Canterbury Plains from Tuesday morning.
FENZ callouts
Fire and Emergency shift manager Simon Lyford said strong winds rolled a truck's trailer and blocked State Highway 8 near Lake Tekapo shortly after 7am on Monday.
A photograph posted on the Tekapo Community Facebook page showed a Mainfreight truck across both lanes of the highway bridge with the trailer on its side on the roadside barrier.
Lyford said the strong winds that caused havoc across much of the South this morning had blown the trailer over.
NZ Transport Agency Waka Kotahi early this afternoon said the winds were hampering efforts to remove of the trailer, but in an update about 2.45pm said the highway had reopened.
Aurora Energy said more than 200 customers in Roxburgh were without power after vegetation hit a power line, but power had been restored to most properties.
Further south, Lyford said crews had already been called out to multiple reports of roofing iron being lifted or blown around near Invercargill and Riverton.
In Tihaka, a Riverton fire crew helped to secure a sheet that had come off a roof and flown across the road about 7am, he said.
Cancellations and delays
At least seven flights have been cancelled in the South Island.
Air New Zealand said five Dunedin flights had been cancelled and two in Invercargill due to high winds.
On Monday morning Wellington Airport said there had been one diversion and two flights landed on the second attempt.
An airport spokesperson said winds were expected to be strong on Monday and Tuesday.
"Most flights should be fine but as always, we advise travellers to keep an eye on our website for flight details and to check with their airlines for the latest information," the spokesperson said.
One of the flights which landed on the second attempt has been confirmed to be an Air New Zealand flight.
The East by West Ferries are meanwhile running a restricted timetable between Days Bay and Queens Wharf due to the weather.
It had also cancelled all sailings to Matiu/Somes Island.
The Cook Strait Ferries are running as usual and no alerts had been issued for Metlink buses or trains.
Power outages across South
More than 700 people in Mosgiel and Dunedin have lost power.
Aurora Energy said crews were investigating the cause.
The areas affected include Mosgiel, Waitati, North Taieri, Outram and Momona.
More than 200 people in Roxburgh lost power when vegetation hit a power line.
Aurora Energy said power had been restored to most of those people.
Further south, PowerNet is investigating power failures across the Riverton and Invercargill area.
While Wellington Electricity is urging people to secure loose outdoor objects and expect power outages.
Wellington Electricity said people should expect power outages from the likes of falling tree branches and other debris.
It was encouraging people to make sure trampolines and other outdoor objects were secured for safety, and to prevent them from damaging property and overhead electrical equipment.
'Could be dangerous'
West Coast Emergency Management is closely monitoring the incoming bad weather.
Manager Claire Brown wanted people to secure their properties, prepare for possible blackouts and avoid unnecessary travel.
She said for people camping and travelling, being caught out in an exposed area tonight could be dangerous.
Teams are on standby to respond.
While in Taranaki, roadworks are continuing on state highways as the clean up for last week's heavy rainfall continues.
Flooding and slips closed parts of State Highways 3, 4 and 43 last week.
"There's still a lot of cleanup ahead, with work underway to assess the damage from slips and work towards repairs," system manager for Taranaki and Manawatū-Whanganui Liesl Dawson said.
All state highways are now open, but the Transport Agency said crews continued to assess damage and clear away debris.
Between New Plymouth and Waikato crews will be working along SH3, along with stop/go traffic management in place and temporary speed restrictions.
"There will be long delays to journey times of around 30 minutes, so please plan your trips accordingly," Dawson said.
More heavy rain has been forecasted for the region later in the week.
