Christchurch suffered 21 lightning strikes after an unpredicted thunderstorm rolled across the city.
Weatherwatch had forecast a gusty southwest change this morning would bring rain, briefly heavy for a time - but not a thunderstorm.
MetService described the thunderstorm as "fairly active" and that the wet, wild and windy conditions were a result of a strong southerly change.
But weather radars detected the storm only at the last minute.
The first strike hit the Garden City at 5.45am, and 20 more strikes followed within an hour.
About 3100 homes in Clifton, Redcliffs and Sumner lost power briefly from 6am, but electricity has now been fully restored.
Just almost as quickly as it came, the front moved up the southeast of the South Island.
The Fire and Emergency New Zealand attended to two thunder-related alarm activations but both were false alarms.
The weather was expected to ease by midday and clear tonight.