New Zealand deployed gunships and helicopters to deliver water, food and fuel to cities cut off by Cyclone Gabrielle on Thursday, as overwhelmed authorities embraced overseas offers of help.
Five people have died, 100 are missing and 10,500 more have been displaced in a disaster that has crippled the country's populous North Island.
Four days of violent winds and lashing rains caused landslides and widespread flooding that lacerated the island's road network, caused rolling power cuts and knocked out hundreds of mobile phone towers.
On Thursday, the east-coast city of Napier was cut off again after experts detected damage to the last useable bridge linking its 65,000 residents 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.
Around the city, petrol stations have put up signs declaring there is "NO FUEL" for anyone other than emergency services.
Prime Minister Chris Hipkins on Thursday warned New Zealanders of a long, gruelling recovery ahead, with power not expected to be restored to some areas for weeks and the clean-up 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."
"There are no overnight fixes. We could have the bulldozers working 24/7 and it would still take time to re-establish road links."
After offers of help from the US and other countries were initially set aside, Hipkins said: "We are accepting offers of international assistance."
The New Zealand Defence Force has deployed two large naval vessels and a C-130 Hercules transport plane to deliver thousands of litres of water along with personnel and several mobile water treatment plants to hard-hit regions.
NH90 helicopters have brought in supplies and rescued hundreds of people stranded on their rooftops.
The cyclone itself has already faded into the South Pacific, but further downpours are expected Thursday, complicating relief efforts and potentially sparking new landslides.
Authorities are still grappling with the scale of the devastation wrought by the storm, and estimates of the damage done and cost of repairs are scarce.
"We know it's going to be in the region of billions, not millions, of dollars," Kiwibank chief economist Jarrod Kerr told AFP.
"I think the figure will be in the range of several billion – five to 10 billion dollars (US$3-6 billion, RM13.21-RM26.41 billion), possibly more."