McDonald's serves a bitten Big Mac!

McDonald's has apologised to an Auckland woman who was served a cold Big Mac with a bite already taken out of it.

Lakyn Allen ordered the burger at Lincoln Rd McDonald's in Henderson on Sunday and said she was "shocked" and "appalled" to find someone had already bitten into it.

McDonald's staff initially disputed the complaint but a review of CCTV footage showed the pre-munched burger being served.

"My first reaction was I just thought this can't be real," Allen said. "I showed it to my partner.

We were both shocked." McDonald's apologised to Allen on Tuesday and said the burger was served as a result of "human error".