Songvut Manoonpong, president of the New Zealand Thai Society, said many in the community had been donning black since their king's death.
"Many consider him to be like a father, and even though nearly a year has passed he is still very dearly missed," he said.
"There is a huge amount of sadness and love still for the late king."
From temple staff to restaurant operators, many have ditched their colourful and flamboyant outfits for black, white or sombre colours.
The mourning period will end only after the royal funeral next month.
The nation of 67 million people and Thais around the globe plunged into mourning after the king's death last year after a long illness.
Manoonpong said all celebrations and events in New Zealand, including Songkran or Thai New Year, had been cancelled or toned down.
"Many of us don't celebrate our birthdays and even weddings have been postponed," he said.
"Only after the king's funeral next month, then you will see people wearing colours and smiling again."
Saturday's event at Mt Eden will give the community a final chance to come together to pay their last respects before the royal funeral.
Saturday was to have also been the last day in Thailand for people to visit the royal urn, but Thailand's King Maha Vajiralongkorn had ordered an extension to next Thursday.
Tens of thousands had been lining up in Sanam Luang to meet the initial Saturday deadline.
Vachanonda, a retiree, still vividly remembers the time she met the late king in Phuket when she was just 10.
"I was part of the welcome party and we were dancing for him, and I felt so proud," she said.
"After I finished my dancing, I rushed to see him and I remember the queen asking 'are you tired from the dancing?'."
Vachanonda, a Thai Society board member, was in Auckland when she got the news that Bhumibol had died.
"I just broke down and cried because he means so much to me," she said.
For the past year, Vachanonda has offering prayers for the late king at the Kelston Thai temple and would prostrate before the late king's portrait in respect.
She will return to Thailand on October 22 to join the official ceremony to farewell Bhumibol.
Before his death, Bhumibol had held the title as the world's longest-reigning living monarch.