"Everyone will think that was rigged, but it wasn't," Mr Cairns told the Bay of Plenty Times.
The port's container terminal opened 25 years ago.
In 2008 it cracked the 500,000 container barrier. In the next decade volumes doubled and the port overtook Auckland to become New Zealand's busiest port by container throughput.
Over the past six years the port spent $350 million to ready itself for bigger ships and larger cargo volumes.
Tauranga MP and Transport Minister Simon Bridges called the port "a star in the system" and praised its investment in infrastructure.
He said the million containers achievement was a win for Tauranga, the Bay of Plenty, and for New Zealand.
Tauranga mayor Greg Brownless said the milestone was recognition of the hard work that had gone into making the port "the best in the country".
Zespri supply chain general manager Blair Hamill said the port was a critical cog in New Zealand's kiwifruit business, and it was great to see it growing.
"The Port of Tauranga is a great partner of ours. They provide a first-class service."
The futures of the businesses were tied together, Mr Hamill said.
Shane Dufour, chief executive of Mount Maunganui-based import/export company Dominion Salt, said the port was an enabler for the business.
The company's export business was growing at a rate of 15 per cent a year.
There were many factors involved, but the port's increased capability and efficiency was a big one.
Ngai Te Rangi chairman Charlie Tawhiao attended the event in spite of some residual tension over the iwi's harbour blockade protests last week, which delayed ships.
"Ngai Te Rangi's relationship with the port has survived the disruption over the weekend," Mr Tawhiao said.
He said the iwi had known the protests would "step on a few toes" but they had a message to get across.
"Mark [Cairns] was understandably pissed off."
Mr Cairns joked in his speech that he was pleased to welcome just the three Tauranga Moana iwi - no Hauraki iwi.
Port of Tauranga by the numbers
6000km - length of 1 million containers laid end to end, twice NZ's length
$350 million - port spend to become "big ship" capable
43% - estimated portion of the region's GDP the port contributes
12,000 - shareholders in Ports of Tauranga Limited
54% - portion owned by the Bay of Plenty Regional Council
190.3ha - port land in Tauranga
14.5m - depth of channel in Tauranga Harbour after dredging
Source: Port of Tauranga Ltd
Emotional attachment to regional ports "wasting money" - port chair
"Emotion and parochial behaviour" by regional port owners is wasting ratepayers' money around New Zealand and threatening long-term infrastructure planning.
Port of Tauranga chairman David Pilkington shared that opinion in a speech at the million-container event at the port yesterday.
New Zealand had "a proliferation" of container ports, he said, with some 13 regional ports.
He believed the Tauranga port's success in attracting bigger ships would trigger a change in that arrangement.
"The introduction of a hierarchy of fewer hub ports and second-tier feeder ports, supported by more coastal shipping, is unquestionably the way of the future.
"Unfortunately, there are ample signs that is not yet fully grasped.
"Ports in general sit in local government ownership and are viewed emotionally as essential to regional development.
"We continue to see plans to pour ratepayers' capital into ports that have little chance of returning the cost of that capital."
He said the Port of Tauranga's public/private partnership was a success, delivering "substantial benefits" for Bay of Plenty ratepayers.
The port still had room to grow, he said.
"We are far from reaching capacity. We have over 30ha we can further develop."
