Updated February 20, 2018 16:27:54

Photo: Air New Zealand says extreme weather conditions have made it too dangerous to fly. (ABC News: Jonathon Hall)

Air New Zealand has cancelled all flights in and out of Wellington, and Christchurch has declared a state of emergency, as the remnants of Tropical Cyclone Gita pummel the country.

Even before the storm hit in full force, heavy rains in the centre of New Zealand brought floods in Christchurch, prompting a warning from Mayor Lianne Dalziel.

"The full impact of the storm will be felt overnight and tomorrow morning," she said, urging residents of low-lying areas to evacuate.

"We are expecting homes to be flooded."

The national carrier said all flights to the capital would be grounded from 2:45 pm (local time) as weather authorities issued warnings of severe weather, with heavy rain and gusts of up to 150 kilometres per hour.

Prime Minister Jacinda Ardern told reporters that military had been deployed to areas likely to be worst hit and the country's national Civil Defence and Emergency Management office in Wellington was on standby to help local authorities.

"My message still to people is please look out for your local warnings and expect disruption to travel and please just be careful," she said.

Some regional airports, including Queenstown and New Plymouth are also experiencing disruptions, according to the Air New Zealand website.

Cyclone Gita hit the Pacific island nations of Fiji and Tonga last week, packing winds up to 275kph and causing widespread destruction and flooding.

It had earlier caused extensive damage in Samoa and American Samoa.

The cyclone has since been downgraded to a storm, but forecasters have warned it is still likely to wreak havoc as it traverses the centre of New Zealand, parts of which are still reeling from a huge storm that prompted authorities to declare a state of emergency at the start of February.

More than 40 schools and preschools have been closed in the upper South Island, while local mayors urged people not to leave their homes.

Transport authorities shut a stretch of highway along the east coast of the South Island and the Department of Conservation was closing picturesque seaside hiking tracks and campsites along the West Coast and ushering tourists away from low-lying areas, media said.

ABC\Reuters

Topics: cyclones, cyclone, new-zealand, pacific

First posted February 20, 2018 13:02:02