Black ice around Waldronville, Green Island, Kaikorai Valley and the hill suburbs caused chaos, with 15 crashes reported to police.
The driver of a milk delivery truck escaped injury when the truck flipped on its side after hitting black ice in Kaikorai Valley Rd at Burnside at 6.30am.
Police also attended three car crashes close to each other in Brighton Rd, near Allen Rd.
One motorist received minor neck and back injuries.
About 8am, there was a three-car pile-up and a car ploughed into the back of a truck after hitting ice in Wakari Rd near Taieri Rd.
A section of the road, between Taieri Rd and Gilkison St, was closed for several hours because of black ice.
Senior Sergeant Mel Aitken, of Dunedin, said warnings urging extreme caution were issued as soon as police became aware of the situation, she said.
Ambulances were called to some of the crashes, but there were no reports of serious injury.
If people felt they could not drive to the conditions they should find another way to get to work, Snr Sgt Aitken said.
Reilly's Towage manager Brian Lilley described the morning as "bedlam".
Every available tow truck driver was called in to help collect nine cars during a two-hour period.
Four of the cars were towed from Wakari Rd and three from Brighton Rd.
"It was different from last month [when Dunedin experienced a heavy snow] because that was over a whole day, where this was in two hours".
A MetService spokesman said black ice was clear ice that took on the colour of the surface on which it lay.
It was dangerous because it was particularly slippery and difficult to see, making the road look as though it was simply wet.
It could form at an air temperature of about 2degC if the ground was particularly cold and was more likely to happen in sheltered areas.
The air temperature was about 5degC in Dunedin at 7am yesterday, but the temperature on the ground was likely to have been several degrees colder, he said.
Dunedin City Council roading and maintenance engineer Peter Standring said the unforecast frost also caught contractors unawares.
Foremen were out checking the roads at 4am, but at that stage it was drizzling and they were not aware it was about to freeze.
By that stage, it was too late to apply the chemical de-icing agent calcium magnesium acetate (CMA), so grit trucks were sent to the affected areas from about 6.30am, he said.
