Emergency services in Rotorua were run off their feet with nine crashes and six people injured in one day.
Heavy overnight frosts left the roads icy yesterday morning as temperatures plummeted to -1C. The icy conditions contributed to at least four crashes.
Senior Sergeant Denis Murphy, who leads the Rotorua police traffic unit, said drivers needed to slow down and drive to the conditions.
"Black ice can be very unforgiving and we've had some very lucky people today, because it really could have gone either way."
He said, in winter, people needed to watch their stopping distances and be aware of their behaviour on the road.
There were three separate crashes in quick succession on State Highway 5 south of Rotorua about 5.30am.
Murphy said they were caused by black ice on the road, driver inattention and not driving to the conditions.
"Two were single vehicle crashes and one was a bus which crashed into a fire appliance already at the scene."
Fire and Emergency Central Lakes area manager Jeff Maunder said it was a "glancing graze" to the appliance.
"There was no damage to the truck, just to the bus."
He said these crashes were what happened when people did not take care on the road.
"Understand we are in winter, and you can't keep driving like we're in summer.
"I don't think it's going to get any less cold, so take a bit more time, look out for ice and stay aware."
At 6.55am a car crashed on State Highway 30 in Tikitere, between Curtis Rd and Lake Okataina.
Murphy said no one was injured in the collision.
Shortly before 9am a truck and van collided on the Rotorua side of Fitzgerald Glade.
The truck was blocking the road and the driver had moderate injuries.
Murphy said the driver of the van had to be cut free by the fire brigade which also cleaned up spilled diesel.
One lane of the road had reopened when a second crash happened, at 9.50am, nearby on SH5, involving two cars and leaving three people with moderate injuries.
Leidy Monslaves was headed to Matamata when she was stopped by the blocked road.
"We were stuck for more than 20 minutes then we saw police racing off to the other crash."
She said it was "really icy" out on the road and the grass was completely white.
"When I got out of the car, it was really slippery.
"It is scary being out on the road like that, there are a lot of drivers who still go too fast."
At 10.50am police were called to the scene of another crash on Gordon Rd in Western Heights, where a car had hit a power pole.
The road was closed while Unison dealt with the power pole and lines which came down across the road.
Tylan Moulder, 17, was driving behind the car that crashed.
"I was behind her, I thought she was turning and she went straight up the kerb and into the power pole.
"The lines came down and it was all on my car, tangled up."
She said it was a complete shock because everything had been normal before.
"The car was smoking, I ran over and there were two kids in the car with her."
At 2pm a vehicle crashed into the lake near Sulphur Point.
The single occupant of the car was uninjured.
Police said the cause of the crash was likely inattention, not driving to the conditions and driving on the wrong class of licence.
The ninth crash happened at 4.05pm when a van and motorcycle crashed on Te Ngae Rd, near Hamiora Pl.
A St John spokeswoman said a man was taken to Rotorua Hospital with moderate injuries.
MetService meteorologist John Law said Rotorua was in for a few more frosty mornings.
"With the water that's come through ground surfaces are wet and dropping to -1C or -2C.
"Those are the perfect conditions for cold and icy roads."
He said the temperature had peaked at 10C today but would drop again overnight meaning more icy patches in the morning.
The cold weather would continue through to Saturday morning and he urged drivers to take care on the roads.
New Zealand Transport Agency Bay of Plenty systems manager Rob Campbell said there were a number of crashes in the vicinity of Rainbow Mountain this morning caused by black ice.
"This area is not commonly affected in this way, and once we were made aware of the issue our supplies applied grit to remove this risk.
"We will continue to monitor this location and treat it appropriately to prevent black ice forming."