Tongan King George Tupou V.
The king died aged 63 at a Hong Kong hospital on Sunday, during a visit to the city.
He will be remembered for bringing democracy to the South Pacific archipelago after taking power in 2006.
New Zealand's Prime Minister John Key paid tribute on Monday.
SOUNDBITE) (English) PRIME MINISTER OF NEW ZEALAND, JOHN KEY
"He was the architect of, the evolving democracy in Tonga, and played an instrumental role in making that happen, and obviously a great legacy for, you know, someone who the Tongan people love very much."
Tongan rugby players arriving in Hong Kong for a match said the king's death would make playing difficult.
The Oxford-educated king gave away his power after pro-democracy riots killed eight, ending 165 years of feudal rule.
Tonga, over 2,000 km northeast of New Zealand, comprises 170 islands and has a population of about 100,000.
Jessica Gray, Reuters