"It's a spectacular success," he said.
"It's fantastic to see the achievement of those taking part, from the elite to those just new to it. And having so many people here to support them and cheer them on, that's really special."
The first full marathon competitor to cross the finish line, in a speedy 2 hours and 27 minutes, was Masataka Uchino from Japan, closely followed by Nelson's Phil Costley who finished just two minutes later.
The fastest female marathon runner was Tauranga's Sally Gibbs, who won the women's title ahead of fellow Tauranga athlete Jess Ruthe.
The crowd cheered loudly as they sprinted across the finish line.
Mr Fleming said the crowd and the 600 volunteers spread across the course played a key role in keeping competitors motivated and energised, which was important.
He said the feedback he had received from volunteers, supporters and competitors was incredibly positive, with a lot of them saying it was better than any sporting event they had ever been to.
"The Rotorua Marathon really is something unique. We're certain it's going to have a long and successful life. It'll no doubt be around in another 50 years time."
He said this year's marathon was expected to have injected $15m in the Rotorua economy.