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RNZ said shifting Concert to the AM frequency would free up space for the broadcaster to build a new music brand for younger audiences.
However, there's been a pushback from Concert fans, with thousands signing an online petition against the move.
Composer Claire Cowan said RNZ was turning Concert into an automated jukebox type service.
"They're proposing a sort of jukebox type system where they have a playlist and it is streaming all the time with no presenters.
"We're not going to be able to get it in the car, it's not going to be great quality. We're not going to have the insight of presenters giving us context and connecting our listeners with the music," she told Morning Report.
"It's going to be a great loss for the classical and art sector in New Zealand."
She said it was Concert where she grew to listen to more classical music, eventually having her work published on the channel too.
In the biggest overhaul of its music services in years, RNZ is proposing to remove Concert from its FM frequencies and transform it into an automated nonstop music station which will stream online and play on AM radio.
It would be replaced on FM by a service aimed at a younger, more diverse audience as part of a new multimedia "music brand".
Concert would be taken off FM radio on May 29 and the youth platform would be phased in ahead of its full launch on August 28.
Announced earlier this week, the move would eliminate 17 jobs at RNZ Music, including all Concert presenter roles, from late March.
Those would be replaced with 13 jobs at the new youth platform, while four remain in the downsized RNZ Concert service and RNZ Music in Wellington.
"There's been a fair bit of feedback over the last 48 hours, some of it has been directed to me, some of it has been directed to Radio New Zealand.
"We have outlined some concerns to them last week, and we're working on it. They are, by law, independent in their programming and operation decisions."
The Spinoff managing editor Duncan Greive said there had long been a case for a publicy-funded youth-targeted station, but starting it in 2020 was a huge risk.
"It's not an impossible task but building a new audience and what is perceived as a legacy medium, when you're trying to attract a young audience could seem a bit wrong-headed."
Former Prime Minister Helen Clark also added to the chorus of concern on Twitter.
She said the marginalisation of RNZ Concert equated to a dumbing down of cultural life in New Zealand.
There was no need to "destroy" Concert to establish youth radio services and broaden audiences, Clark said.
While its listenership is predominantly Pākehā and skewed towards older people, the new music brand would target people aged 18 to 34, including Māori and Pasifika audiences, the RNZ proposal states.
"We are thinking five and ten years ahead. We need to start to connect with younger New Zealanders," RNZ chief executive Paul Thompson told Mediawatch.
He said RNZ Concert's classical music focus has prevented RNZ from fulfilling its Charter's requirement to broadcast a range of music and performances.
"We are expanding our services off our current resources. There are some tough choices in that but this is a really good story of RNZ getting to more New Zealanders," he said.