A number of staff from the New Zealand Defence Force have been stood down after an alleged incident involving an unknown substance while on an operation in Fiji.

A spokeswoman at the Defence Force confirmed five staff were stood down from their normal duties yesterday while an investigation was in progress.

She said the incident didn't affect the humanitarian support currently operating in Fiji in the aftermath of Cyclone Winston last month.

With wind gusts of up to 230km/h, Cyclone Winston was recorded as the strongest tropical cyclone to ever make landfall over Fiji.

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It killed 44 people, damaged or destroyed nearly 25,000 homes and affected about 40 per cent of the population.