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A lightning strike cut power to much of the Wellington region last night.

The cut happened shortly after 11pm and the Kapiti Coast, Porirua and the Hutt Valley were affected, a Wellington police communications spokesman said.

Vector Electricity said power was cut to between 30,000 to 40,000 homes.

Power was restored to Lower Hutt after a short period but other areas were without electricity for up to three hours.

Traffic and street lights were plunged into darkness from Waikanae to Wellington's Ngauranga Gorge but no major traffic problems were reported. The strike came as the southern North Island prepared for severe weather to signal the end of summer.

The Met Service forecast severe northwest gales today for the southern North Island and heavy rain for the Tararua and Ruahine ranges and Mt Taranaki today, as well as further south in Buller where up to 100mm could fall in the middle of the day.

For the North Island from Taranaki and Hawke's Bay south, damaging wind gusts of up to 130km/h were forecast and a strong wind warning was in place.

Transpower spokeswoman Rebecca Collerton said they could not confirm lightning or heavy rain had caused of the blackout but they were the prime suspects for the problems at the substation at the bottom of the Hayward's Hill.

Paraparaumu down to Johnsonville was affected from about 11.15pm until 1.15am.