Nearly $2 million is expected to be injected mostly into the Otago economy by delegates from as far afield as China, Lithuania and Russia attending the fifth Global Botanic Gardens Congress in Dunedin in October.
So far, 238 people have registered for the event, part of Dunedin Botanic Garden's 150th anniversary.
Dunedin City Council project manager Hamish Black said the largest number of registrations had come from the United States (49), Australia (41) and New Zealand (37).
There were also registrations from Europe, Thailand and Malaysia.
''We're very excited about it, as it gives us a real chance to showcase Dunedin.''
It was hoped 300-350 people would register for the congress, being held at the Dunedin Centre. Many of the international delegates had indicated they were planning to see more of the South Island before or after the congress, he said.
In preparation for the bid for the conference in 2009, Conference and Incentives New Zealand estimated the conference would draw 450 delegates and generate $2.9 million to the New Zealand economy, with the bulk spent in Dunedin.
However, as the world economic situation had not fully recovered from the global financial crisis, delegate numbers were downgraded to about 300 so the economic impact was likely to be $1.9 million-$2 million, he said.
The Dunedin City Council had granted $70,000 over three years towards the cost of the conference. Fundraising was being carried out to raise any additional money required, he said.
So far, $30,000 had been raised and congress organisers were looking for more contributions ''big or small'', Mr Black said.
''The money is going to help run the congress and ensure we make this a special event for the delegates, the botanic garden and, ultimately, the city.''
A day of field trips was planned to places such as Macraes and Strath Taieri, and there would be sightseeing tours before and after the congress.
Work was also under way to make it a community event involving local entertainment and students, he said.
