Air New Zealand engineers are at Hawke's Bay Airport carrying out an examination of one of the engines on an ATR72 aircraft which had to be grounded mid-morning after a light haze was detected in the cabin prior to take-off.

An Air New Zealand spokesperson said the engineers arrived to carry out checks early this afternoon.

It was not known what had sparked the haze but smoke had been ruled out.

"Not sure at this stage what it was," the spokesperson said.

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"The engineers are onto it."

The aircraft had been scheduled for the NZ5210 flight from Napier to Auckland and after the haze was detected it was cancelled and passengers taken off.

"Everyone was re-booked on available services," the spokesperson said.

It was not known how long the aircraft would be grounded for at this stage.