Those with an eye on the sky in Auckland on Thursday morning may have noticed something large swooping over the city just after 7am.

A massive Soviet Antonov-124 freighter aircraft, one of the largest in the world, arrived in New Zealand from Hawaii and is reported to have transported an America's Cup challenger.

The aircraft is about 70m long with a wingspan of 74m and can carry more than 400 tonnes of cargo.

Aircraft of this size are often used to transport concert stage set-ups and equipment - one of the last Antonov-124 visits to Auckland was to carry Taylor Swift's tour gear.

While no one was officially commenting on the purpose of the aircraft's arrival, just like the cargo this Antonov was carrying, any plans to keep its visit unnoticed, were foiled. Photos posted on social media last week show the same Antonov aircraft on the ground at Rhode Island being loaded with America's Cup challenger American Magic.

With the reported cargo likely to be valued into the tens of millions of dollars, one can only hope they were using more than bubble wrap for the 20 or so hours of flying time to Auckland.

The yacht is thought to be moving to its new home on the city's waterfront before the massive aircraft leaves Auckland empty.