The power was off for about 15 minutes but Mr Mahon said no danger was caused to people on the rides at the time.
After travelling from Waipakarau to the show for the past 50 years, Annabelle Hamilton said this year's show was the best yet.
"All the young ones come and it's marvellous," Mrs Hamilton said.
She was cooling off inside the Taste Hawke's Bay pavilion around the food stalls that had been taken indoors this year for the first time.
It was not all fun and games though, Mr Key stepped aside to discuss some hot issues before he left.
He said he supported the Ruataniwha Dam, noting water storage facilities were important to Hawke's Bay.
Mr Key said the region was extremely productive and "produce[d] some of the greatest agricultural products in the country".
In the wake of a dry El Nino, the potential of a summer drought was a concern.
"We've certainly been supportive of water storage schemes and irrigation schemes and we think Ruataniwha is very important."
Mr Key also touched on the recent controversy around changes to gun-purchasing laws.
He said a review of the laws was still underway but for now the recent alterations were sensible.
