New Zealand's prime minister says Cyclone Gabrielle, which has pummelled much of the North Island, is a weather event not seen "in a generation".

Chris Hipkins' government has declared a state of emergency - only the third in New Zealand's history.

About a third of the country's population of five million people live in affected areas.

Many people are displaced and some were forced to swim from their homes to safety after rivers burst their banks.

Others have been rescued from rooftops.

About a quarter of a million people are without power. Falling trees have smashed houses, and landslides have carried others away and blocked roads.

The storm's damage has been most extensive in coastal communities on the far north and east coast of the North Island - with areas like Hawke's Bay, Coromandel and Northland among the worst hit.

Communications to one town in the region have been completely cut after a river burst its banks.

Civil defence authorities in Hawke's Bay said they couldn't cope with the scale of the damage. Australia and the UK have pledged to help.

A firefighter remains missing after being caught in a landslide in Muriwai, west of Auckland. A second firefighter involved was critically injured, rescue agencies said.

Marcelle Smith, whose family lives in a cliff-front property in Parua Bay on the east coast of the North Island, told the BBC she had fled inland with her two young children on Monday night.

Her husband remained behind to set up protections for their home. Some embankments set up had already been washed away and they were still battling wild weather on Tuesday.

"We are trying to do everything we can to protect what we have put our lives into. It's man versus nature at this point," she told the BBC.

Local media have reported that some residents in Hawke's Bay had to swim through bedroom windows to escape as waters flooded their homes. People have been warned they could be without power for weeks.

Aerial pictures of flooded regions showed people stranded on rooftops waiting for rescue.

The vast scale of the damage includes uprooted trees, bent street lights and poles, and row after row of flooded homes.

New Zealand's Defence Force released dramatic pictures of officials rescuing a stranded sailor, whose yacht was swept out to sea when its anchor cable snapped amid strong winds.

"The severity and the damage that we are seeing has not been experienced in a generation," Mr Hipkins said on Tuesday.

"We are still building a picture of the effects of the cyclone as it continues to unfold. But what we do know is the impact is significant and it is widespread."

He has pledged NZ$11.5m (£6m; US$7.3m) in aid to support those affected by the disaster.

Declaring the national state of emergency on Tuesday morning, the Minister for Emergency Management, Kieran McAnulty, described the storm as "unprecedented".

The emergency order enables the government to streamline its response to the disaster. It has been applied to the Northland, Auckland, Tairawhiti, Tararua, Bay of Plenty, Waikato and Hawke's Bay regions.

New Zealand has only previously declared a national state of emergency on two occasions - during the start of the Covid-19 pandemic and following the 2011 Christchurch earthquake.

The government has attributed the scale of the disaster to climate change.

"The severity of it, of course, [is] made worse by the fact that our global temperatures have already increased by 1.1 degrees," said climate change minister James Shaw.

"We need to stop making excuses for inaction. We cannot put our heads in the sand when the beach is flooding. We must act now."

Cyclone Gabrielle has hit New Zealand just two weeks after unprecedented downpours and flooding in the same region, which killed four people.

The MetService says conditions are expected to clear in coming days, and heavy rain warnings are being lifted for some parts of the country. But it has warned that wind could still cause further damage.