The firefighter was checking flooding in a property on Motutara Rd on Monday, when the property was hit by another house that collapsed during the widespread winds and rains unleashed by Cyclone Gabrielle.
A second firefighter, Craig Stevens, who was in the property at the time got out and was taken to hospital. He is now in critical but stable condition.
In a written update from Fire and Emergency New Zealand (Fenz) on Wednesday just before 11.30am, they said their teams alongside police had found the body in the Motutara Rd search area.
"We have not yet identified who this is and will be working with police to retrieve and identify the body.
"We will provide more information later today. I acknowledge the difficult time this is for all of us, particularly for family, the Muriwai Volunteer Fire Brigade and all at Fire and Emergency New Zealand."
Fenz asked people to respect the involved families' privacy.
In an update from the government on the cyclone response before midday, Emergency Management Minsiter Kieran McAnulty and Defence Force Minister Andrew Little extended their condolonces.
"Our deepest condolences to the family, to the community, and to all volunteers and emergency services - this will no doubt hit hard," McAnulty said.
Earlier on Wednesday morning, crews had resumed the search for the firefighter after having to abandon it on Tuesday night when darkness fell, due to safety.
At the time, Fenz chief executive Kerry Gregory said they held out hope to find the firefighter.
"All of our brigades are very much like families, so it's like losing a family member. So it's going to be a long healing process for brigades, because we don't lose firefighters every day. This is really a rare event for us."
Crews had removed 2000 cubic metres of soil and debris, picked apart a house piece by piece and used various means like thermal imaging, a K9 dog, and listening devices to try and locate the missing firefighter.
Other properties on Motutara Road were evacuated too after the slip, and Auckland Council's emergency management team on Tuesday asked property owners in the worst-affected parts of Muriwai to consider their own safety and stay out of their homes for the time being.
