A passenger has died during a 12-day cruise sailing from Sydney to New Zealand, sparking an urgent investigation.

Police were notified of a unexplained death on the Anthem of the Seas traversing New Zealand on Wednesday around 1.40am.

Officers are investigating the circumstances.

The ship carrying more than 4000 passengers and 1500 crew was bound for Waitangi in the Bay of Islands. 

It left Sydney on March 22, according to the website Cruisemapper, before reaching New Zealand on Wednesday.

The Daily Mail has contacted the operator Royal Caribbean for comment.

Royal Caribbean offers cruises to luxurious locations such as the Caribbean, South Pacific, Australia and New Zealand. 

More to come. 

A passenger has died at the start of a 12-day cruise sailing from Sydney to New Zealand