15 (Reuters) - Cyclone Gabrielle weakened and moved away from New Zealand on Wednesday as the country started to assess the damage caused by significant flooding, landslides and high winds that left four people dead and displaced thousands from their homes.

Gabrielle, which reached New Zealand on Sunday before making its way down the east coast of the North Island, cut off entire towns, washed away farms, bridges and livestock, and inundated homes, stranding people on roof tops.

"We thankfully are through the worst of the storm but we're not out of danger yet," Emergency Management Minister Kieran McAnulty said during a televised media briefing.

"This is a significant disaster and is going to take many weeks for those areas most affected to recover ... we are in this for the long haul."

Residents in hard-hit areas are now being asked to conserve water and food because of fears of shortages after the cyclone forced New Zealand on Tuesday to declare a national state of emergency for only the third time in its history.

Police on Wednesday said four people had now been confirmed dead including a volunteer firefighter who responded to a call out and was caught in a landslide on Monday.

Around 1,400 people have been reported as having not been in contact since the cyclone, but police said they expect this is due largely to communication lines being down.

However, the statement added that police do hold "grave concerns" for several missing people.

Parts of New Zealand's North Island, where about 75% of the country's 5 million residents live, are enduring their second major storm in as many weeks. Record rains last month triggered flash floods in Auckland and four people lost lives then.

Authorities estimate more than 10,000 people have been displaced so far.

Helicopters winched people stuck on rooftops to safety, while military planes will be used to deliver essential supplies to isolated towns, McAnulty said.

Alysha Haidekker was back assessing the flood damage at her home in badly hit Hawke's Bay on Wednesday. The water has drained away but it has left silt, swollen wood and damaged her new kitchen, wall linings and doors.

She said they'd managed to move a lot of their belongings to an upper storey but the flooding happened fast.

"The water was coming in the door and I panicked and tried to get a towel but by the time I turned around I could tell a towel was not going help," she said. "It had just started seeping in from every courner."