Prime Minister John Key believes the days of free to air coverage of major sports events are probably over.

New Zealand First has called on the government to step in to ensure "showpiece" sports events, such as All Blacks tests, are broadcast free.

MP Clayton Mitchell said “hundreds of thousands will miss out on watching the game live on television because they can’t afford to pay a monthly fee to Sky."

But Mr Key told Mike Hosking the financial side of modern sport makes free to air All Blacks matches unrealistic.

"The rugby live is on Sky, and I don't know what the Rugby Football Union earn from those broadcasts but they're huge."

Key said this income is vital for high performance sport.

"There's so much money that go into providing both the pay and the other benefits that are required to have these athletes at a world class level."

WATCH MORE: Mike Hosking's full interview with PM John Key