New Zealand's shipping federation say coastal transport is a resilient lifeline during natural disasters such as earthquakes.
However, it says not enough attention has been paid to ensuring ports are up to the task.
Shipping Federation executive director Annabel Young said coastal shipping had picked up in the wake of earthquakes.
It had highlighted the need for more investment in ports, especially roll-on roll-off ferry services.
"The ship route from Auckland to Lyttelton takes about 38 hours in the Spirit of Canterbury. That is about the same as if you went from road, to rail, to ship and then back onto rail," she said.
"Taken with international ships, you have got about a ship a day leaving Auckland for Canterbury, so ships can take up the slack but they are reliant on ports being available.
"Both Picton and Wellington were able to get up and running with their roll-on, roll-off services very quickly," Ms Young said.
"If either of those ports were taken out, there is an alternative in Nelson, but I am not sure where you would go in the North Island."
The earthquake damaged Wellington's container terminal, but ferries and cruise ship activities had recovered.
Government agencies have debated the vulnerability of the wharf as a whole.
Cook Strait services transport goods worth $15 billion to $20bn annually. That equated to 30-40 percent of the value of New Zealand's total goods exports. About 820 people were employed in the ferry operations.
University of Canterbury geological sciences professor Tim Davies said coastal shipping had advantages.
It could carry heavy goods and had a lower carbon footprint.
Mr Davies said most upper South Island roads were too vulnerable to seismic damage.
Before the 14 November earthquake, State Highway 1 through Kaikōura was the best, but it was not good enough considering its importance to the South Island economy, Mr Davies said.