SYDNEY, Feb 12 (Reuters) - Residents of New Zealand's biggest city were urged on Sunday to prepare for the impact of a storm that buffeted Australia's Norfolk Island overnight.

Gabrielle, downgraded to a sub-tropical low pressure system from a Category 2 cyclone, passed over Norfolk Island, its "most destructive winds" missing the island, the Australian outpost's emergency management authority said.

The focus shifts to New Zealand, 1,460 kilometres (910 miles) south, where the nation's weather forecaster warned of the storm's impact from Sunday. Last month the largest city, Auckland, was hit by record rainfall that sparked floods and killed four people.

The city of 1.6 million was in line for a "full trifecta" of heavy rain, strong winds and storm surges, said Georgina Griffith, a spokeswoman for the forecaster, MetService.

"Don't be fooled if you're not affected until Tuesday," she told reporters.

Wind and rain were "starting to spread across NZ from the north", with a 133 kph (83 mph) wind gust reported overnight on the country's North Island, MetService said.

Auckland Emergency Management warned the city was likely to be hit by strong winds on Sunday night, with gusts of up to 140 kph (90 mph) or higher from Monday.

With Gabrielle closing in, Air New Zealand said it was cancelling multiple long-haul international fights on Monday, as well as Tasman and Pacific Island flights, and domestic services in and out of Auckland.

Mayor Wayne Brown's office urged residents to prepare, including by tying down loose outdoor items and ensuring houses were clear of debris.

The storm was on track to lie off Cape Reinga at the North Island's north end on Sunday afternoon, after moving away from Norfolk Island, MetService said.

On Norfolk Island, which covers just over 34 square km (13 square miles) in the Pacific Ocean between New Caledonia and New Zealand, authorities said they were clearing debris and trees from roads and restoring power knocked out in the storm.

"There is still considerable clean up to be undertaken and it may take a while for services such as power to be restored," Emergency Management Norfolk Island said.

Its roughly 2,000 residents, some descended from British sailors who mutinied on the HMS Bounty in the 18th century, had been "extremely fortunate" with the passage of the cyclone, the agency said, as winds eased and an all-clear was issued.