Fire and Emergency (FENZ) has confirmed that the person taken to hospital in a serious condition was a firefighter, who suffered a medical event while battling the SkyCity convention centre blaze.
St John Ambulance said a further three people were treated at the scene for minor injuries.
- Live updates: Huge fire breaks out at SkyCity convention centre
- Watch: Dramatic footage shows smoke billowing across Auckland city
- SkyCity convention centre fire: Photos and videos
- 'It was hot against the windows': Witness in nearby building on SkyCity fire
FENZ public information manager Thomas Harre said the firefighter suffered an unrelated medical event while working to extinguish the blaze in Auckland's CBD on Tuesday afternoon.
The blaze has now been contained and emergency services are working to defend the neighbouring buildings - yet the fire is still burning.
"It's under the roof and on the roof... it's in a very difficult place at the construction site, as it's semi-built it adds to the complexities of firefighting," said Harre.
"We'll remain present on site well into the night and early morning to monitor it."
- SkyCity convention centre fire: Commuters warned to avoid CBD due to gridlocked traffic, smoke inhalation
- As it happened: One person unaccounted for as emergency services 'at capacity' to contain blaze
Harre said it's difficult to determine the extent of the damage due to the thick smoke.
The cause of the fire remains unconfirmed, although it has been reported that an unattended blow torch may have started the blaze.
"I can confirm our fire investigators are on sight... they'll do a full investigation when the fire is extinguished," Harre told Newshub.
FENZ is unsure how long the SkyCity evacuation will last.