New Zealand's Lyttelton Port and Port of Otago are moving to the next phase of merger talks.

"The boards of the ports have agreed to continue to work towards a potential operational merger," the companies said in a joint statement.

The next stage involves talks on the content of a report prepared by Antipodes Capital as part of the first stage of the project.

The structure being considered involves the legal separation of the infrastructure assets from the operations and commercial activities of each port.

Any agreed proposal for an operational merger would ultimately require shareholder support and approval from the Commerce Commission, the competition regulator.

Ports are looking at merging so they do not over capitalise when preparing for the next generation of large container ships. Talks between Port of Tauranga and Ports of Auckland in the North Island failed.