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Mr Cull, who is heading an 11-member Dunedin delegation in Shanghai this week, was the only member of the group invited to the opening of the inaugural China International Import Expo yesterday.
Mr Xi opened the week-long expo with a keynote speech, extolling the virtues of trade liberalisation, globalisation and the continuing economic opening up of China.
He also took a swing at US President Donald Trump's "America first'' policies and threats of import controls by saying the the world's multilateral trading system "should be defended''.
The event has attracted world leaders and more than 3000 businesses from 152 countries, including New Zealand.
Mr Cull, who watched Mr Xi's speech, said it was a "big deal'', offering an alternative to protectionism and challenging the "zero sum nationalist sentiment'' of President Trump.
"[It was] momentous in that Xi is arguably the most powerful man in the world, issuing a major strategic challenge.''
The expo, which included a global forum on developing and enhancing world trade and the commercial system, was the first stop on a week of meetings for Mr Cull and the Dunedin delegation.
After meetings with representatives from the Shanghai Arts & Film Federation and business and education sectors yesterday, the itinerary for the rest of the week included a mix of civic meetings and agreement signings.
On Thursday, that would include signing a new sister school memorandum of understanding between Guangming High School and Otago Boys' High School.
Enterprise Dunedin would also sign a partnership agreement with Guangming High School, while an agreement with the Shanghai Education Commission would be updated.
At Yu Yuan Garden, the group would attend the opening of a photographic exhibition marking the 10th anniversary of the opening of Dunedin's Chinese Garden.
The group will also meet representatives from the Shanghai Foreign Affairs Office and Jiaotong University before departing for Dunedin.
Joining Mr Cull on the trip are deputy mayor Chris Staynes, Enterprise Dunedin director John Christie and three other Enterprise Dunedin staff members.
The University of Otago's international office, food science department and language centre and foundation were also represented, as was the Dunedin Chinese Garden Trust and Dunedin Shanghai Association.