Sewage overflows, surface flooding, slips & road closures, and unfortunate incidents like the train collision north of Plimmerton - http://www.stuff.co.nz/national/4184297/Trains-collide-near-Porirua.
Some very quick thinking on the part of the staff on the trains probably prevented serious injury. The drivers were very lucky to escape with their lives.
The rain is expected to ease after midnight, thankfully.
EDIT: More on the train collision - http://www.stuff.co.nz/national/4186110/Landslide-causes-derailment-collision
And more on the weather-related incidents - http://www.stuff.co.nz/national/4186094/Weather-keeps-emergency-services-busy