The Maori king has extended his personal condolences to the royal family and people of Tonga on the death of King George Tupou V.
The 63-year-old king died in a Hong Kong hospital on Sunday.
The Kingitanga and the Royal House of Tonga have had strong links for many years.
In a statement, King Tuheitia says he is shocked and saddened by the death and that the hearts and thoughts of Kingitanga go out to all the people of Tonga at this sensitive time.
Both King Tuheitia and King George Tupou ascended their thrones within months of each other in 2006.
The Tongan king was a guest at the first Koroneihana celebrations at Turangawaewae the following year.
The statement says both monarchs have remained close friends and confidants.
King Tuheitia will attend the state funeral for King George Tupou.