Vector said crews were working on the faults but were having to battle heavy traffic to get to some of them.
Spokeswoman Sandy Hodge said all lines should be treated as live, and any lines brought down by lightning should be reported to 111.
weather conditions were expected to ease for most places from 6pm, WeatherWatch said.
Isolated showers - some heavy - will remain this evening and clear overnight.
MetService meteorologist Rob Kerr said thunderstorms would move from Taranaki to Waikato and across Auckland to parts of Northland.
Lightning was possible, as were hail stones between 5mm and 10mm in diameter.
Gloaming, if the gloaming is something you can have in Devonport. pic.twitter.com/KFTa4bRaN2
@WeatherWatchNZ hailing in the affluent seaside suburb of Milford. I won't tolerate it.