An Auckland man has admitted having two wives.

Rodney Peach, 52, originally from South Africa, admitted one charge of bigamy and one of knowing that a document including details of marriage was forged, when he appeared in Manukau District Court on Tuesday, Fairfax Media reported.

Peach was accused of marrying Trisha Faiainoa while still married to Tania Peach, his wife of 28 years and who now lives in Australia.

The couple have two children and are legally separated.

According to Rainey Collins Lawyers bigamy is a punishable crime because it is thought to represent a threat to public morality and to compromise the institution of marriage.

The second marriage is considered the crime, no matter where in the world it takes place.

The only defence is if the first spouse has been absent for seven years, and is believed to be dead.

The maximum term of imprisonment is seven years if there is an attempt to protect an innocent party to a bigamist marriage.

Peach will be sentenced on February 10.