Royal Australian Navy submarine spotted in Auckland harbour

A submarine has been spotted in Auckland this morning. Photo: Mark Unwin / Twitter

A submarine has been spotted in Auckland this morning.

But there's no need to worry, it's just the Aussies dropping in for a party.

The HMAS Dechaineux has popped across the ditch to celebrate the 75th anniversary of the Royal New Zealand Navy.

A witness told the Herald that she saw what she believed was a big, black, military-sized submarine cruising near Queens Wharf and past the Ferry Building about 10.30am.

The HMAS Dechaineux is a Collins Class diesel-electric submarine, one of six operated by the Royal Australian Navy.

It is 77.8m long with a beam of 7.8m, a draught of 7m and a top speed of 20 knots (37km/h).

A member of the public has tweeted an image of the Australian submarine.

@nzherald Submarine spotted in Auckland Harbour about 30 mins ago. pic.twitter.com/7a30ylWb4g

— Eddie (@softwaresalmon) November 2, 2016

Though not everyone was as excited.

Disappointed the submarine spotted in Auckland Harbour doesn't look like this. pic.twitter.com/TDzaaSPVXx

— Sam Farrell (@SamFarrellNZ) November 2, 2016

At least 15 countries will participate in the International Naval Review, to celebrate the Navy's 75th - including a long list of defence and security force personnel, ships and aircraft.

That's something you don't see every day - submarine in Auckland harbour pic.twitter.com/53XtbrhUoV

— Chilly of the Valley (@samfinnz) November 2, 2016

The review begins on November 17 and vessels will berth at either Ports of Auckland or Devonport Naval Base.

The biggest event of the birthday celebrations is the International Naval Review in Auckland.

As well as the entry of the fleet into Waitemata Harbour on November 17, a '1000-sailor' march down Queen St is planned for November 18.

On November 19, the formal International Naval Review will be held, during which Governor-General Dame Patsy Reddy will review the assembled ships, in a centuries-old naval tradition.

Vessels attending the party include Canada's Frigate HMCS Vancouver and a CH124 Sea King helicopter; Chilean tall ship Bach Esmeralda; and Japan's destroyer JS Takanami.