Fruit growers in New Zealand’s Hawke's Bay have highlighted the biosecurity risk as being too big to justify an international airport at Napier.

MPs have proposed an extension of the runway by 600 metres, to give the airport capacity to take commercial jet services.

But Hawke's Bay growers believe the increase in international traffic would raise the risk of introducing pests into the environment with potentially devastating effects for their industry.

Hawke's Bay is the largest top fruit and stone-fruit growing area in New Zealand.

"Why would we introduce the risk into such an important horticultural and agricultural area?" asked Bridge Pa grower Jonathan Wiltshire.

The discovery of salt marsh mosquito just north of Napier illustrated the possible downside, he said. Five exotic ant incursions were also recorded at the Port of Napier in January.

Wiltshire also doubted there would be the volume of traffic to justify the extension. "How many people would really want to fly directly from Napier when it is two hours to Palmerston North and four to Hamilton international airports?

“And as a frequent overseas traveller the cost of flying out of Hawke's Bay to reach an international airport is a negligible part of the overall cost," he told the local media.