Trade and craft shows and private events such as weddings, most of which would have would have been at the showgrounds' Waikoko Gardens, have also been postponed.
The Hawke's Bay A and P Show has been the region's biggest annual event for many of the past 156 years, attracting more than 40,000 at its peak. Foot traffic last year was about 28,000.
The show was for many years one of the select group of five sharing the hosting of the Royal Agricultural Society's Royal New Zealand Show, effectively a national championship of show stock classes and first held in 1924.
But it has been held at Showgrounds Hawke's Bay Tomoana each year since 2015, and the A and P Society has a current contract with the RAS to stage the show until 2022 and a right to renewal that could take it into the Royal Show's centennial year.
Hawke's Bay A and P general manager Sally Jackson said that although the 2020 show is still scheduled to go ahead, she can't see it happening if a level 4 or level 3 Covid-19 alert continues. It's only a maybe even if it's downgraded to Level 2 or Level 1.
"No one's told us what a level zero would look like," she said. "We are very much relying on guidance from the Government."
She said that in the meantime it had to be "business as usual", although it's difficult making the contracts with exhibitors and other show sponsors and supporters when not even the businesses have any certainty about whether they'd be able to exhibit if the show goes ahead.
She said the impact of cancellations is "huge" for not-for-profit organisations such as the society, which relies "100 per cent" on its event.
"It's a massive thing," she said.
She said that as a "recovery" event – in an era being compared with the all-hands-on-deck post-war years – the society would be "very, very keen" to stage the show to help "bring everything back to normal".
"Events will be key to that recovery, and we would all be craving community interaction," she said.
The society would have to consider cost-saving measures such as including the Primary Sector Awards in its show-week package.
Ewan McGregor, who wrote the society's history for the 2013 celebration, noted the decline of A&P shows over the years in competition with big industry and trade-focused events such as agricultural field days. He said new ideas were needed to make the event relevant for town and country.
The show is the first of each summer's four-show package in Hawke's Bay. The Central Hawke's Bay A&P Show is scheduled for mid-November, the Wairoa show for January, and the Dannevirke show for the first week of next February.