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Trade of new and used cars valued at $2 billion through the Ports of Auckland would be thrown into chaos by the proposed waterfront stadium, according to shipping companies.
The Government has proposed that the stadium be built over the water between Bledisloe and Captain Cook wharves - wharves predominantly used for unloading vehicles.
Shipping lines Armacup, Kiwi Car Carriers and Toyo Fuji dock at the wharves targeted for the stadium and represent 70 per cent of the new and used vehicle trade through the port.
The companies are linking to fight against the stadium and are holding an urgent meeting this morning with Rugby World Cup Minister Trevor Mallard.
Kiwi Car Carriers chief executive Terry Riches said there was no other viable place to berth its ships at any port around New Zealand, including Ports of Auckland.
The Government has said work should start on building the stadium in May.
"It will leave us without any berths or storage facilities in less than five months ... nowhere in fact to offload the 15,000 vehicles, trucks and equipment that comes into Auckland each month," said Mr Riches.
Ports of Auckland has told the shippers that no acceptable alternative proposal for the docking of the ships had been found.
Armacup Maritime Services executive chairman Mark Ching said the port struggled to manage the flow of cargo as it was at full capacity.
The Port of Tauranga has said it would accommodate the shipping lines if the stadium went ahead.
But Mr Riches said he "was not certain" there would be room at Tauranga because it would eventually compete for space with other vessels.
"I do believe that there will be major congestion around the stadium which will displace the container and bulk ships as well," he said. It was possible they would have to move to another port.
About 85 per cent of the vehicles that come through the Ports of Auckland go to caryards in South Auckland, he said.
If the shipping lines were forced to another port, such as Port of Tauranga, trucking companies could add at least another $250 to the price of new and used cars for the transport to and from Auckland, Mr Riches said.
And the lines estimated it would add about 40,000 truck movements to the road between Tauranga and Auckland.
It would be almost impossible for rail to cope.
"Our only expectation would be road transport," Mr Riches said.
"There will be serious congestion on that route. It could also make life more difficult for the import and export car companies, largely based in Auckland." He described the stadium proposal as an "economic disaster".
"Officials need to come to their senses and see this plan for what it is - an impossible dream. Economically, socially and politically, this stadium simply does not float."
The shippers first heard about the proposal when it went to a Ports of Auckland meeting last Monday.