Road users are urged to take extra care across the Waikato and Bay of Plenty state highway networks, with below-zero temperatures expected overnight and snow, frost and ice possible across both regions.

The entire network is expected to be cold, with particular care needed on State Highway 30 (SH30), SH36 and SH38, SH2 Waioweka Gorge and SH5. Extra care on SH1 south of Tokoroa, SH4, SH46, SH47 and SH49 is also urged.

Crews are also on standby on State Highway 5 Napier-Taupō Road tonight, with snow and ice predicted to low levels.

NZ Transport Agency Waka Kotahi (NZTA) contractors will monitor conditions and lay grit or anti-icing agents where needed to help keep people safe. Snow is already present on the network, drivers who encounter maintenance vehicles should stay a safe distance behind and not pass unless instructed.

Black ice is a thin, transparent layer of ice that freezes over the road and can be difficult to spot. Ice is more likely to form on bridges, in shaded areas and other places that receive little sunlight, but icy patches can occur anywhere when temperatures fall below zero.

Drivers are urged to reduce their speeds, increase their following distances and avoid sudden braking or turning movements on icy roads. Use dipped headlights in foggy or low-visibility conditions, allow extra time and check weather and road conditions before heading out.

People travelling early in the morning should be prepared for conditions to change quickly and drive to the conditions at all times.