New Zealand's grape harvest is 9 per cent down on last year's, mostly due to bad weather, NZ Winegrowers said.

The 2017 Vintage Survey showed the harvest totalled 396,000 tonnes.

"Given strong demand in overseas markets, wineries had been looking forward to a larger harvest this year," NZ Winegrowers chief executive Philip Gregan said.

"With the smaller vintage however, export volume growth is likely to be more muted in the year ahead," he said in a statement.

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Generally summer weather was very positive but there were some challenges as the season progressed, Gregan said.

In terms of vintage quality, wineries were confident the vintage would deliver the fruit flavours that New Zealand wine is known for.

Reports from across the wine regions indicate that generally wineries are positive about the vintage quality.

"However, as always the ultimate test will be how the market reacts to the wines when they are released," he said.

"At this stage we are confident the 2017 vintage wines will add to New Zealand's reputation as a premium producer of cool climate wines."

New Zealand wine is exported to more than 90 countries and wine exports are currently valued at $1.65 billion per annum.

Wine is New Zealand's 5th biggest export good.