Chief of Defence Force Lieutenant General Tim Keating said Passchendaele evoked the worst memories of World War I.
"Passchendaele was a tragedy that left scars that have endured for generations," said Keating.
"It remains a stark reminder for those of us in the New Zealand Defence Force today of our responsibility to care for those who serve and the families who support us."
Sergeant William Wilson, a New Zealand clerk, said the Battle of the Somme was "pretty bad I'll admit" but Passchendaele was worse.
"I have never seen such destruction," he wrote.
"It is hard to imagine that four years ago, peaceful people tilled this same soil, that it was one of the most prosperous districts in Europe. Now, as I saw it today, well it's simply an awful nightmare, a hideous reeking swamp seething with living (and dead) beings. A place that stamps itself on one's mind and memory like a red-hot iron."
In spite of the enormity of the disaster, many New Zealanders today will know little of the disaster, yet be well versed in that other World War I tragedy, Gallipoli.
Passchendaele Society President, Iain MacKenzie says the Battle of Passchendaele is of immense significance to all Kiwis.
"One hundred years ago, our men fought, died and witnessed unspeakable horror some 18,500km away from their homeland. They fought alongside our Allies for the freedom which we take so much for granted today," MacKenzie said.
"It was a day which has greatly influenced our sense of national identity and the development of our nation.
"We can look back on those dark days with respect for the fallen, and we can also look forward, with commitment to sustaining the peace that these men fought and died for.
"There are a great number of activities happening in regions and cities throughout New Zealand and indeed the world, to remember the Battle of Passchendaele and the courage and bravery of those who fought on the Western Front during World War One. I encourage everyone to join in."
Commemorative events in New Zealand
Thursday, October 12
Commemorative service at Auckland War Memorial Museum run by the Passchendaele Society 10am: In front of the Cenotaph, 2,412 personalised white crosses will be installed, commemorating the New Zealanders who lost their lives in the entire Passchendaele Offensive period from July 31 to November 8, 1917. At 11am, there will be a Battle of Passchendaele 100th Anniversary Commemoration Service in the Auckland War Memorial Museum's WWI Hall of Memories.
National Ceremony and Belgian Memorial unveiling at Pukeahu National War Memorial Park in Wellington 3pm: All are welcome to attend. Live streamed on ww100.govt.nz and its Facebook page. At 6pm a musical tribute, Remembering Passchendaele: Our Darkest Day will be held at Te Papa's Wellington Foyer just outside the Gallipoli exhibition, featuring the Royal New Zealand Air Force Band.
Saturday, October 14
Ghost soldiers Queens Gardens, Dunedin 12pm: A live action tribute to the Otago soldiers who lost their lives at the Battle of Passchendaele. Ten volunteers dressed as soldiers will slowly walk through central Dunedin from Knox Church to Queens Gardens on October 14 singing NZEF songs, talking among themselves, and resting, while acting as if there is no one else around them. If approached they will hand you a bereavement card, carrying the name of one of the many Otago men who fell at Passchendaele.
Commemorative events in Belgium
Wednesday, October 11:
Menin Gate Memorial to the Missing 7pm-8.30pm: A special ceremony with a distinctly New Zealand flavour will be held along the ramparts of the moat around the Menin Gate before the New Zealand Defence Force contingent takes part in the traditional Menin Gate Last Post Ceremony. The memorial is dedicated to the more than 54,000 British and Commonwealth soldiers who were killed in Leper and whose graves are unknown, including many New Zealanders who served with imperial or Australian units.
Thursday, October 12:
New Zealand National Commemorative Service, Tyne Cot Cemetery 11am: The New Zealand National Commemoration for the Battle of Passchendaele at the largest Commonwealth War Grave Cemetery in the world. There are 198 named and 322 unknown New Zealanders buried in the cemetery and 1166 New Zealanders are commemorated on the Memorial to the Missing. At 3pm, the New Zealand Passchendaele Centennial Memorial & Garden will be opened at the Memorial Museum Passchendaele.
Sunset Ceremony at Buttes New British Cemetery, Polygon Wood 7.30pm. It will tell the story of Passchendaele through a narrated arrangement of music, poetry and ceremony featuring the New Zealand Defence Force's musicians, Māori Cultural Group and military ceremonial personnel. The arrangement will depict the effect of the conflict on the soldiers and their families at home.