Locals in the vicinity of the Marsden Point oil refinery in Northland had a spectacular show tonight as the facility flared off gases.

A huge fireball was seen at the plant, 30km southeast of Whangārei.

A refinery spokesman said at about 10pm the refinery had an issue during the restart of the hydrocracker unit and as a safety precaution shut the unit down.

"Residents in the area will have seen a flare at the refinery.

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"The flaring is a safety precaution to allow the safe venting of refinery gases during the shutdown of this unit.

"There is no harm to staff or to the plant and we are in the process of investigating."

Northland fire crews were called to provide assistance at 10.15pm, a Fire and Emergency spokesperson said.

Local fire crews were asked to be on site as a precaution but had been stood down by 11.40pm.

The refinery also has its own firefighting crews on site, the refinery spokesman said.