The country's petrol stocks have jumped significantly with several big shipments on the way to New Zealand.

The latest government data to midnight on Sunday also shows diesel stocks are up slightly, while jet fuel is down.

There are 59 days' of petrol, 45.2 of diesel and 50.2 of jet fuel either in the country or on the way.

That's compared to the previous update: 51 days' of petrol, 44.3 of diesel and 54.1 of jet fuel.

The government said the increase in petrol stocks was due to several large shipments recently embarking for New Zealand - and the decline in jet fuel was anticipated following recent high stock volumes.

It said further shipments were planned, and fuel was continuing to arrive regularly.