Officials have confirmed the potential new flag waving atop the Auckland Harbour Bridge is the wrong colour and will be replaced.

Hoisted alongside the present flag, the huge Kyle Lockwood fern and Southern Cross design contains the wrong shade of blue and will go within the next seven days.

"The fabric weight and printing technique used to produce the alternative flag flying on the Auckland Harbour Bridge has resulted in a lighter blue than the silver fern flag eligible voters will consider in the final referendum," a NZ flag consideration project spokeswoman said this evening.

"The NZ Transport Agency is currently producing one in a different fabric to resolve this. It is being produced as quickly as possible and will be installed next week."

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She said the panel and the agency were "committed to ensuring best colour representation, as well as meeting the exacting conditions for flying on the bridge to ensure traffic safety at all times."

After concerns were raised about the blue hue last week, the panel said large flags could give the illusion of "varying colours in different light levels".