The country's only oil refinery at Marsden Pt has is shut for two weeks while its undertakes planned maintenance.
Refining NZ said units have shut down at Marsden Pt for planned maintenance on the Refinery's Hydrocracker, which began on Saturday.
The two-week pit-stop for a Hydrocracker "top-bed-skim" will allow for maintenance, inspection and repair of equipment that is normally in operation.
Refining NZ chief operating officer, Andrew Brewer said that the planned maintenance on the Hydrocracker was undertaken every other year and was critical for process safety.
"A key part of the top-bed-skim is refreshing the catalyst package in the top bed of the Hydrocracker unit. This keeps the unit running safely and will allow the rest of the catalyst in the Hydrocracker to achieve a three to four-year life."