Kiwis and NZ-based Americans will gather today to mark the 15th anniversary of the 9/11 terror attacks - and pay honour to the lives lost in the heinous acts which shocked the world.

Almost 3000 people lost their lives - including more than 400 police officers and firefighters - during four coordinated terrorist attacks in New York and Washington D.C in 2001.

The catastrophic events led to the War on Terror, the American-led international effort to fight terrorism.

New Zealand firefighters will be the first in the world to hold a memorial event, when more than 160 firefighters from across New Zealand climbing the Sky Tower's 1,103 stairs at 1.30pm.

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The Memorial Firefighter Stair Climb will honour those lost in the line of duty in 2010, with names of the dead featuring on tags being taken to the top of the Sky Tower.

Acting general manager at SkyCity Auckland, Matt Ballesty said the climb allows Kiwis to pay respects to firefighters lost in a "tragic world event".

"As well as many Kiwi firefighters who've lost their lives in the line of duty, but also for us to give back and honour our firefighters and the incredible work they do in our community every day."

United States Ambassador to New Zealand, Mark Gilbert will also be participating in the stair climb.

"I will do it with a full kit, with the firefighters."

Gilbert said the American flag will be lowered at the US Embassy and Consulate in Wellington today, however the staff will not gather until Monday when everyone is present, for a minute's silence.

Deputy Chief of mission for the US Embassy, Candy Green will also be attending the annual memorial at the Firefighters Reserve in Christchurch, where a sculpture dedicated to lost firefighters was built out of steel from the World Trade Centre, in 2002.