"I think the solution for cars is Northport," said Mr Cairns, whose company owns 50 per cent of the business at Marsden Pt.
"We have a yield per hectare of land [in Tauranga] ... and we haven't been able to get cars to stack up.
"If you properly price the cost of capital of this area [Auckland] are you getting sufficient return off that and is that the best cargo use?"
Ports of Auckland spokesman Matt Ball said importing cars through Northland would increase pressure on the roading network and add costs to the supply chain.
The cost of extending the North Auckland rail line to Northport has been costed at $100 million.
David Vinsen, chief executive of the Imported Motor Vehicle Industry Association, was reluctant to see car imports moved from Auckland.
He said there was a large industry set up, principally in South Auckland, to deal efficiently with the importation and processing of vehicles.
Trains could not carry cars through tunnels from Northland, he said, which would mean up to 70,000 truck movements on SH1.
Michael Goldwater, of the anti-port expansion protest group Stop Stealing Our Harbour, said importing cars was a poor economic use of prime Auckland real estate.
It might avoid truck movements between Auckland and Marsden Pt, he said, but those same trucks were going through the city centre.
"Where is the sense of that?" Mr Goldwater said.
Mr Cairns said he could not see a merger between the ports of Tauranga and Auckland, 10 years after talks between the two parties faltered.
He said the opportunity had been lost with the duplication of infrastructure by the two port companies and a growing gulf in market value between the companies.
Neither does Mr Cairns support calls for a national port strategy, saying the last strategy in the 1980s was an abysmal failure.
Mr Cairns did not want to comment on Auckland Council's Future Port Study. "I very much think that is an Auckland matter to consider," he said.
Mark Cairns on ...
Car imports: Move them from Auckland to Northport
Port merger: Lost opportunity 10 years ago
National port strategy: Abysmal failure last time
Future Port Study: A matter for Auckland.