"With Auckland's business growth moving south, and Auckland, Waikato and Bay of Plenty dominating the upper North Island's economic growth, Northport is too far away," the report said, while moving to Whangārei would add more than 125,000 tonnes of carbon dioxide per year for container road freight, compared with about 27,000 tonnes from Ports of Auckland to South Auckland.
That would seriously undermine New Zealand's efforts to reduce greenhouse gases, it said.
"The decision to move the port from Auckland to Northport is being rushed. We need to stop. Take stock. Reassess," the report added.
But Brown said the association had a vested interest ensuring that the port didn't move north.
He described claims about greenhouse gas emissions, as "total and absolute crap," saying goods transported to and from Northport by rail freight would mean less pollution and traffic congestion.
"At the moment, more stuff goes to Auckland from Tauranga, which is further away from Northport. Milk from Northland goes to Tauranga for export," he said.
"Auckland is planning 50,000 houses in the south and 86,000 houses north of (the city). Where are the biggest new commercial businesses like IKEA and Costco going? To West Auckland, not south," Brown said.
He led the Upper North Island Supply Chain (Unisc) working group, whose report promised an economic boom for Northland if the $10 billion port move happened.
"There's nothing that will make Northland do better than shifting the port from Auckland," he said.
Smith said the days of Ports of Auckland were numbered, whereas Northport offered the best deepwater port in the upper North Island.
"Everyone is aware of the growth in Waikato and further south, but the next era of growth in New Zealand will, in my view, be on the north side of Auckland," he said.
"Ships will be getting bigger in future, and the risk for New Zealand is they won't be able to come here. That's where the deepwater port at Northport has an advantage."
Regional Economic Development Minister Shane Jones said the report was built around fear and apprehension, citing points of weakness in the state of the trucking industry.
"We'll see more electric trucks in future, but for now we see a significant role for rail, and I think the trucking industry is churlish in not acknowledging the $700 million put aside for a four-lane highway out of Whangārei heading south," Jones said.
Through its Provincial Growth Fund, the Government has provided $300 million for work on the existing rail line between Auckland and Whangārei.