Five people have been killed and 100 are missing after the storm battered the North Island, home to most of the population.
Five people have been confirmed dead after four days of strong winds and torrential rain. Authorities say 100 are missing and 10,500 more have been displaced.
Prime Minister Chris Hipkins on Thursday warned New Zealanders recovery would take time, with power not expected to be restored to some areas for weeks and the cleanup likely to take much longer.
“This is a traumatic event,” he said. “It’s a very big challenge to restore infrastructure as fast as we can but we have to acknowledge that we are in for a bumpy ride.”
After initially setting aside offers of help from the United States and other countries, Hipkins added: “We are accepting offers of international assistance.”
The New Zealand Defence Force has deployed two large ships and a C-130 Hercules transport plane to deliver thousands of litres of water along with personnel and several mobile water treatment plants to the most hard-hit regions.
It has also used helicopters to deliver supplies and rescue hundreds of people stranded on their rooftops.
On Thursday, Napier was cut off again after experts detected damage to the last bridge linking the town’s 65,000 people with the rest of the country.
Isolated residents have been told not to leave their homes unless “absolutely essential” and to restrict water use.
When residents do venture out, they wade through murky floodwaters to get supplies or huddle on the steps of a few buildings that still have WiFi, trying to get in touch with loved ones.
Hipkins said people’s inability to get in touch with family and friends was a real issue and the government was working on immediately increasing connectivity.
Earlier on Thursday, Finance Minister Grant Robertson said the country was financially able to meet the costs of rebuilding.
Parts of New Zealand’s North Island, where about 75 percent of the country’s 5 million residents live, are enduring their second big storm in as many weeks. Record rains last month triggered flash floods in Auckland and four people were killed.
Meteorological service MetService said Cyclone Gabrielle is now east of the country and continuing to track away from the North Island. However, it said thunderstorms might hit badly affected areas of Hawke’s Bay and Tairawhiti on Thursday.
New Zealand declared a national emergency over the storm on Tuesday, only the third time it has ever done so.