Freezing night ahead
Temperatures are set to dip again tonight, after a southerly front brought snow across parts of the South Island.
This afternoon there were still some snow flurries about Banks Peninsula, and some snow was visible on the Port Hills.
MetService meteorologist Elke Louw said parts of the South Island would be set for a chilly start tomorrow, with a low of -9 degrees Celsius expected for Twizel.
Christchurch would be slightly warmer on -5C in the morning, with Ashburton on -3C.
Temperatures would remain low during the day, Louw said, with a high of about 10C across the region.
Police warned drivers to keep a close eye on road conditions, with frosts and snow possible in Canterbury.
Senior Sergeant Phil Newton of Canterbury Highway Patrol warned drivers to adapt to the wintery conditions.
Frosts are likely tomorrow morning, particularly inland.
"That's going to make many roads across the district treacherous, and will dramatically increase the risks of drivers having a crash - especially if they have a lapse in concentration," he said.
''Our most important message to all drivers is to slow down whenever the weather turns bad.''
Newton recommended drivers increased following distances, cleared ice and condensation from their windscreens and checked the tyres, brakes, lights and windscreen wipers on their vehicles.
Drivers on the mountain passes should carry chains.
Arthur's Pass and Haast Pass were both reopened yesterday after slips closed them last week.
A ''massive slip'' about 1 kilometre west of the Otira township closed Arthur's Pass on Friday.
NZ Transport Agency senior network manager Mark Pinner said the highway would remain open overnight
Single-lane access through the area was opened at about midday. Traffic through the area was being controlled and limited to 30 kph.
National Institute of Water and Atmospheric Research (Niwa) data shows the coldest temperature recorded in Christchurch during May last year was -2.8, recorded near the airport on May 30.