She said it was a great opportunity for local retailers to take their shops to "where the crowds are".
"There's potentially 25,000 people going through that event centre in two days ... you wouldn't get that in your shop."
Ms Kai Fong said runners and supporters would be at the centre registering on Friday and would be there from early on Saturday morning.
And while the runners made their way around the lake, their supporters would be looking for things to do, she said.
In previous years there had just been displays by a couple of sponsors so this year was a first, Ms Kai Fong said. "I took the idea [of the expo] to Event Promotions as an add-on to the marathon by having a full expo," she said. "It's the 50th so it's something a bit special, a bit different."
She said several tourism operators had recognised the opportunity. "It's a marketing exercise for them. Even if [visitors] can't visit that weekend, they know next time they come back the wonderful things to see and do," she said.
"We're using this as an opportunity to promote Rotorua."
She said a local real estate agency would be there, seeing it as a chance to show the Auckland contingent what their money could buy them in Rotorua compared with Auckland.
"It's selling that whole work, live, buy [in Rotorua] thing."
Ms Kai Fong said the city would be buzzing over the whole weekend and she had been talking to CBD businesses about making the most of it, right from the Thursday when visitors began arriving in town.
That included putting extra staff on and staying open longer hours where possible, while banks were preparing to restock their ATM machines more regularly over the weekend, she said.
"If people have a really good time then hopefully people will want to come back."
For information about exhibiting at the expo email skaifong@xtra.co.nz or call Sandra Kai Fong on 027 283 6080. There is a fee for exhibitors although that may be negotiable for community groups.