A new deepwater quay is to be opened at Warrenpoint harbour later, the latest stage in a £21m development.
The new quay creates two new deepwater berths and can handle fully-laden container vessels and other cargo ships of up to 10,000 tonnes.
The harbour has also announced the start of a twice-weekly container service with Cardiff Container Lines.
The total cost of the second phase of the development came to more than £12m.
It follows the opening of a new roll-on, roll-off facility last year.
Warrenpoint Harbour Authority chief executive Peter Conway said the modernisation was vital if it is to continue to meet the demands of a changing market.
"The port is an economic driver for the whole region," he said.
"This latest phase of the development means that the port can continue to play a major role in the local economy."
He said Warrenpoint was now the second port in Northern Ireland with both lift-on, lift-off and roll-on, roll-off facilities.
"Conservative estimates indicate that direct employment within the harbour currently introduces over £3m of purchasing power into the local economy every year," he added.
"Goods handled by Warrenpoint Port have a sales value of over £1bn, 42% of which are exports."