Refining New Zealand has released images of its ruptured pipeline which show, it says, that the damage was caused by a digger.
The damaged fuel pipeline - on farmland in Ruakaka, about 20mins south of Whangarei - was discovered on Thursday a week ago.
It has led to dozens of flights in and out of Auckland Airport being cancelled, affecting the travel plans of thousands of people.
The pipe carries jet fuel from the Marsden Point refinery near Whangarei to Auckland Airport, as well as petrol and diesel for vehicles.
Refining New Zealand said the images showed tooth indentations and scrapping and gouging were caused by digger's bucket.
It said the photos also show where the pipe ruptured after sustaining earlier damage.
Refining New Zealand said it was making good progress and repairs were on-track to be completed between Sunday and Tuesday, although settling and recertification would take another 30 hours.
"The replacement section has been welded into place and the initial weld inspections have passed. This is an important milestone. The second weld inspection will be carried out tonight," it said in a statement.
Meanwhile, Energy and Resources Minister Judith Collins said fuel companies expected to discharge jet fuel and diesel into Wynyard Wharf this weekend, to be trucked to the airport next week.
Mrs Collins said the two trucks had already delivered jet fuel from Marsden Point to the airport today.
She said some petrol stations may run out of 95 octane today as fuel companies focus on supplying 91 and diesel.
Kauri often dug without MPI's knowledge - conservation group
Ms Collins said she has been told by MPI that no swap kauri has been dug on the property where the pipe ruptured since 2011.
But a Northland conservation group said MPI could not know for sure when the site was last dug over for swamp kauri.
The ministry said the only milling statements it has for the site go back to 2011 - but two neighbouring landowners say huge trees were being extracted just two or three years a go.
Northland Environmental Protection Society president Fiona Furrell said people have been digging up swamp kauri in Northland for years without MPI's knowledge.
The Northland Regional Council has begun investigating the cause of the breakage.