The death was confirmed by the Kiingitanga's social media early on Friday morning.
"Kiingi Tuheitia Pootatau Te Wherowhero VII has died peacefully this afternoon, accompanied by his wife Makau Ariki and their children Whatumoana, Korotangi and Ngawai Hono I Te Po," it read, in te reo, the Maori language.
Tuheitia was in hospital recovering from heart surgery.
"It didn't quite go as we had all hoped," the Kiingitanga's chief of staff Ngira Simmonds told Radio NZ.
"In the early hours of this morning he passed away peacefully."
Prime Minister Chris Luxon praised the Maori King's "dedication to Aotearoa New Zealand". (AP PHOTO)
Former prime minister Dame Jacinda Ardern has led tributes to the King, describing him as "an advocate for Maori, for fairness, justice and prosperity".
"You worked tirelessly on building understanding and knowledge of our shared history and in doing so, strengthening Aotearoa."
The Maori King position was founded in 1858, aiming to be a unifying movement for all Maori tribes.
It is a largely ceremonial but hugely consequential role in New Zealand.
In recent months, Tuheitia co-ordinated national unity talks for Maori in response to the centre-right government's policies.
"He believed in the vision of his ancestors. He understood his role and his duties," Mr Simmonds said.
"He wanted to serve and do everything that he could and exhaust every effort to bring unity to our people and indeed the nation at large.
"He served until the very last."
Prime Minister Chris Luxon, who is in Tonga for the Pacific Islands Forum, also paid respects.
"His unwavering commitment to his people and his tireless efforts to uphold the values and traditions of the Kiingitanga have left an indelible mark on our nation," he said.
"I will remember his dedication to Aotearoa New Zealand, his commitment to mokopuna, his passion for te ao M�ori, and his vision for a future where all people are treated with dignity and respect."
Last week, thousands travelled to Turangawaewae Marae for annual celebrations of the King's ascension to the throne.
Maori speakers scolded the prime minister and other ministers for various parts of the government's agenda, including a bill that would redefine the 1840-signed Treaty of Waitangi in modern-day New Zealand.
The seat of the Maori King is held by the Tainui tribes in the Waikato and it is not yet clear who will take the throne.
"The death of Kiingi Tuheitia is a moment of great sadness for followers of Te Kiingitanga, Maaoridom and the entire nation," Rahui Papa, a Kiingitanga spokesman, told TVNZ.
"It is expected that Kiingi Tuheitia will lie in state at Turangawaewae Marae for five days before he is taken to his final resting place on Taupiri Mountain."
Mr Simmonds said the next few days would be for local tribes to mourn.
Others would then be welcomed to the marae, including international dignitaries, followed by a Maori funeral, known as a tangihanga.
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