A lines company says power may be out to some of Napier for two weeks but not for most people.
Of about 40,000 homes without power across Hawke's Bay, almost 32,000 of those are in and around Napier.
Hawke's Bay Civil Defence controller Ian Macdonald told a media briefing that due to the flooding of the Redclyffe substation, much of the region remained without power on Thursday morning, with only about 90,000 homes and businesses currently connected to power.
He estimated power would likely not be fully restored across the region before next Thursday.
Unison said electricity was being progressively restored to them.
The regional council had earlier said online that: "The power outage in Napier is expected to be at least two weeks."
But Unison spokesperson Danny Gough said "two weeks would be the worst-case scenario".
"It's fair to say that it won't be up to two weeks for the majority.
"There's plans afoot as we speak and there's the utmost urgency going into those plans."
Thursday was "a critical day for us", when a clearer picture would emerge about lines down and other damage, Gough said.
The repair bill would run in to the tens of millions of dollars, and insurance cover would kick in, he said.
So far, the city is relying on Faraday Street zone substation, where Gough had been for the last two days.
He applauded Unison technicians who had engineered a clever switch to get emergency power to essential services - a supermarket, health centre and service station.
"They banged their heads together ... I can't thank the guys enough for doing that."
The service station reported running out of petrol. The regional council said fuel supplies "have been secured" and stock would be replenished when the port reopened - at this stage this Friday.
National grid operator Transpower said it was working to route more power through its Whakatu substation northeast of Hastings, and would have an update on that later today.
Gough spoke to RNZ as he was driving on the sole road that reopened between Napier and Hastings Wednesday night.
Authorities are asking people to only make essential trips.
"The road's very busy," with cars rather than trucks, Gough said.
"Clearly people are trying to catch up with loved ones, maybe going over to get supplies at the Hastings."
Out the car window, he could see floodwaters still sitting there - "a helluva mess".
"The rail bridge is completely gone.
"There's some cars that have been obviously abandoned and you can see the water's come right up past the roof of those vehicles.
"It's just unbelievable."
Gough said Unison had flown over parts of the power network outside the cities.
"What we can see from the air is that it is very significant damage with the amount of poles down and broken, and lines down.
"So we're not under-estimating the task of getting into those areas. Good news is access is improving every day" with contractors opening new routes for them, he said.
Power outages elsewhere in North Island
Thousands of homes have no power in the upper North Island.
Meanwhile, 16,000 Auckland households are without electricity, after 9000 were restored yesterday, provider Vector said.
Power has been restored to towns such as Dargaville, but many homes in the surrounding areas are still reporting outages.
In the Far North, almost 4000 Top Energy customers have no power, down from 7500 yesterday.
Power companies are continuing repairs today.
Repair bill for power lines estimated at $100m
The repair bill for power lines damaged by the cyclone is estimated at $100 million.
The Electricity Networks Association said it would be 'a very large number'.
This estimate is for the country's 27 local lines companies and excludes the costs faced by national grid operator Transpower.
Various lines companies not hit by the storm are sending field crews to hard-hit places or offering to take fault and other calls from them.
The association said it had yet to find out what was needed by Eastland Network in Tairāwhiti and Unison in Hawke's Bay, Rotorua, and Taupo.