Auckland's loss may be Tauranga's gain as ships unable to use the Bledisloe and Ferguson container terminals are diverted.

Port of Auckland Ltd is locking out its container terminal workers for two days - Saturday and Sunday, with the workers striking on the Friday and Monday.

These industrial actions follow the breakdown of talks between the port and the Maritime Union.

Port of Tauranga.

Ports of Auckland has announced mediation between the parties failed to produce agreement on the terms of a new collective contract.

More than 300 Maritime Union of New Zealand workers threatened to strike at the downtown Auckland container handling, road and rail services site for two days from 10.30pm on the Friday and Monday.

The lock out is because the maritime workers will not withdraw the strike notice.

The Bledisloe and Fergusson terminals will be closed from 10.30pm on Thursday, December 1 through to 10.30pm on Monday, December 5.

It's likely four ships will divert to the Port of Tauranga and two could miss Auckland from their shipping schedule entirely, says Ports of Auckland chief executive Tony Gibson.

Port of Tauranga acting chief executive Graeme Marshall says the numbers of ships is not determined.

'These are existing customers who would normally call Auckland first and Tauranga last on their schedule so all they would be doing is just diverting,” says Graeme.

'While there may be four ships, we are working with customers and Port of Auckland as well to assist where we can without disrupting our own customers and business.

'We are just working with our customers and trying to understand what the situation is, and how it's likely to develop and what we need to do.”

Ports of Auckland's multi-cargo wharves, cruise business, vehicle import trade, marine services, Onehunga seaport, Wiri Inland Port and Seafuels barge Awanuia are not affected. The on-dock empty container depot will also remain open.