Fire crews tackling the SkyCity blaze are still in "active firefighting mode" and are being confronted by pockets of flames today.
Fire and Emergency incident controller Dave Woon said today's work also included an "overhaul" phase as firefighters pull off iron and roofing and sealing materials from the roof.
Before and after
Woon told reporters that fire crews had done an "outstanding job" as Fire and Emergency NZ released photos from inside the damaged building.
Diversions are expected to worsen rush hour traffic as Aucklanders head away for the Labour Weekend holiday.
SkyCity CEO Graeme Stephens said it would be weeks before the convention centre was secure enough to properly assess the damage, and at least a month or two before they knew exactly how much damage there was.
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Fenz said firefighters were moving to a "recovery phase", which involved finding and extinguishing hotspots in the roof structure as well as any fire inside over the next few days.
That also involved clearing out about eight million litres of water, contaminated by burning materials, that had accumulated in the Convention Centre's basement carpark.
Watercare estimated the firefight had used nearly 30 million litres of water.
Auckland Council's Safeswim manager Nick Vigar said that water had initially been pumped into the stormwater network and out to the Viaduct basin around Beaumont St.
A swimming alert was issued for nearby St Mary's Bay.
By last night it had been transferred to the wastewater network, after Watercare confirmed the Māngere Wastewater Treatment Plant could handle the contaminated water.
A council spokeswoman said they were not sure exactly how much contaminated water had entered the Hauraki Gulf, and water testing was still being completed.
Hauraki Gulf Forum deputy chair Moana Tamaariki-Pohe said the damage to the harbour's sensitive ecosystems could potentially be "devastating".
"It will have huge impacts. Our stormwater system needs to be prepared to handle this so it doesn't happen again. The Gulf is already stressed, and adding all of this contamination is hugely devastating."
The accumulated water had also flooded about 100 parked cars, all belonging to SkyCity staff members.
Stephens said staff would be compensated for any damage to their vehicles.
While emergency services had now entered the fire-damaged convention centre, he had not yet received any direct reports on the extent.
Yesterday they had been focusing on preparing the existing SkyCity sites to reopen, with the casino opening last night, Sky Tower expected to open this morning and hotel this afternoon.
As the casino opened its doors a steady trickle of patrons made their way into building.
A security guard said it was much quieter than usual, but he expected it to pick up later on.
Despite the big clean-up there remained a faint smell resembling burnt plastic through a big part of the building.
SkyCity's relationship with construction company Fletchers was in good shape, Stephens said.
The chances of having the convention centre finished in time to host Apec in 2021 was "not clear", he said.