Light snow was reported in areas including Ranfurly, Naseby and around Millers Flat as winter keeps a grip on the South.
Snow and ice warnings were issued for several sections of southern highways, and State Highway 87 Kyeburn-Omakau was closed for a time owing to ice.
All highways are now open but the New Zealand Transport Agency advises motorists to exercise caution.
- Check highway conditions here
Danseys Pass road is closed.
Further north, hundreds remain without power after Taupo and inland Hawke's Bay were hit by a blizzard over the weekend, Fairfax reports.
Snow between Taupo and Napier caused widespread power outages. Hundreds of power poles were brought down and it could take 10 days for some rural areas to have power restored.
In Otago, while conditions are milder this morning, the severe temperatures that froze part of Otago Harbour and burst water pipes in Dunedin homes and businesses yesterday are forecast to continue for most of the week.
Central Dunedin dropped to -2.3degC and Dunedin Airport recorded a low of -7.1degC.
A cold southerly flow over the whole of New Zealand and clear skies over the South Island created the "perfect conditions" for the big freeze, Mr Glassey said.
A ridge of high pressure moving over the South Island would keep overnight temperatures in the region low until at least Thursday.
Cromwell was expected to record the coldest overnight temperature this week of -8degC tonight.
A front moving on to the South Island on Friday would probably increase temperatures in parts of Otago by 5degC.
The wintry blast kept Dunedin plumbers busy yesterday morning.
Those contacted by the Otago Daily Times reported being inundated with calls about burst water pipes from early morning.
EC Shaw Plumbers Ltd plumber Ken Shaw said he had seen extreme water damage.
"Ceilings have collapsed. People are having to get in electricians to isolate their power."
People could lessen their chances of having burst pipes by leaving a heater below an open ceiling manhole on a cold night, he said.
A plumber who did not want to be named said he attended jobs where whole storeys in a house were "totally" gutted by water.
Fire crews from the St Kilda and city stations attended a sprinkler activation, believed to have been caused by the frost, at Spa Pools Otago in Strathallan St.
St Kilda station officer Howard Weir said he thought the full cleanup would take "ages".
"It will certainly be a setback for them."
Neighbouring shop Dunedin Auto Trimmers 2000 also received water damage because of the activation.
Spa Pools Otago owner Andy Connelly said the shop would not reduce its hours because of the water.
"Being a spa pool business, it means it is not a big deal."
A rugby field-size portion of Dunedin Harbour near the intersection of Portsmouth Dr and Portobello Rd was covered in ice yesterday morning.
Dunedin consultant hydrologist David Stewart said it was "highly unusual" for the harbour to freeze.
In 2005, the Andersons Bay inlet froze.
However, temperatures below -2degC were required to freeze sea water, which was higher in density, he said.
State Highway 88 was described on social media as "nearly impassable" due to ice on Saturday morning, with others reporting near misses and complaining the road was not sprayed with CMA to prevent ice from forming.
A police spokesman said they had received reports of icy conditions but only two crashes were recorded on SH88 on Saturday.
Each involved a single car leaving the road due to ice, and no-one was injured.
An NZTA spokeswoman said SH88 was gritted multiple times from early in the morning on Saturday, but CMA was not used because the road was too wet.
Police urged motorists to take extreme caution and keep a lookout for the blue cat’s-eye devices on roads that indicate icy conditions.
All highways remained open yesterday but winter driving warnings were in place around Otago, the spokeswoman said.
