Sir Howard died in Rotorua today, aged 74.
Mr Key, speaking from New York where he is at the United Nations, says Sir Howard had been at the forefront of New Zealand music for more than 50 years and his contribution was immense.
"Sir Howard was a New Zealand success story. From humble beginnings he became an international success, first with the Howard Morrison Quartet, and then in an illustrious solo career," Mr Key said.
"But more than that, Sir Howard was one of New Zealand's best loved entertainers, his appeal spanning every age group.
"I pay tribute to a real gentleman. My thoughts are with his whanau at this time. Sir Howard Morrison will be greatly missed." Labour leader Phil Goff said Sir Howard was a great New Zealander and a legend of entertainment for generations of Kiwis.
"He has been a huge part of New Zealand life for such a long time and will be missed by us all.
"I would like to extend my sympathies to Sir Howard's whanau for their loss," Mr Goff said.
Rotorua-based Labour MP Steve Chadwick said Sir Howard lived a rich and full life that he shared with the Rotorua community and all of New Zealand.
"Sir Howard loved the song I Did It My Way and he certainly lived up to the words he sung so beautifully," Ms Chadwick said.
"To politicians he was someone who was determined to hold us to account and to keep us honest, but he was always welcoming to us no matter what side of the political divide we were on." Sir Howard had frequent dealings with the political world and was a strong advocate on Maori health, education and development issues.
Last year it came to light that expat billionaire Owen Glenn offered Sir Howard $1 million to stand for Parliament.
"We got on so well he actually offered me a million dollars to stand as a Member of Parliament as an independent. I turned him down," Sir Howard said at the time.
One of Sir Howard's enduring legacies was his encouragement of family into the entertainment business.
He sang at the launch of young relative and now rising international soprano Elizabeth Marvelly's self-titled debut album two years ago.
Marvelly's father, Rotorua hotelier Brett Marvelly, said he rang her in Germany this morning to tell her of the news of Sir Howard's death.
"She is, of course, very sad. She had a very strong emotional connection to him, she respected him so much for all the right reasons ... He taught her so much." In recent years Elizabeth Marvelly had toured extensively with Sir Howard and Dame Malvina Major and was among those who performed at a televised concert staged in Rotorua in his honour last year.
TVNZ said today it would rescreen the programme, To Sir With Love, on TV One tomorrow at 8.30pm.
Sir Howard, who had a history of heart problems, died in Rotorua this morning. He had recently returned from a holiday in Rarotonga.
He had a singing career for more than 50 years, gaining fame as his Howard Morrison Quartet ran up a string of hits in the late 1950s and 1960s.
He was awarded an OBE in 1976 and was knighted in 1990. Of mixed Maori and Pakeha ancestry, Sir Howard was born in 1935 into a Rotorua family renowned for its entertainment skills. He was married to Kuia, Lady Morrison, for 52 years. They had two sons and a daughter.
