The celebrated GP and health advocate, who was 82, died on Friday night after contracting COVID-19.
Dr Williams had more than 50 years' experience as a GP, medical researcher and health advocate.
He spent 25 years in the Cook Islands and served as a Cabinet Minister for six years before becoming prime minister in 1999.
More recently he had been practising medicine in Auckland. Pasifika Medical Association president Kiki Maoate, who is also Dr Williams' nephew, said his uncle was driven by his determination to serve his Cook island community, even well into his advanced years.
Maryann Heather, a doctor at Southseas Healthcare in Otara, has known Dr Williams since she was a medical student.
She said he was an inspiration and a mentor for many Pacific doctors and his death is a huge loss.
It was also a reminder of the risks the COVID-19 virus poses to vulnerable communities.
"We never want anyone to be a fatality but it just highlights the uncertainty around this pandemic and we need to just take it seriously."
She urged people in vulnerable groups, including Māori and Pasifika, to remain extra vigilant and get tested if they have any symptoms.
Clinical psychologist Jacqui Maguire said Dr Williams death is bringing the COVID-19 pandemic closer to home for many people in this country.
She said it's likely his death will feel bigger than some others in the pandemic and will likely increase worries in the community.
She advises people feeling anxious to focus on what they can control, such as physical distancing and hygiene measures.
"I urge New Zealanders to acknowledge how they're feeling; to do the best they can to stay calm; and to try and not extrapolate from this casualty that COVID-19 in New Zealand is bigger than it is right now."
COVID fatigue has been high and this is a very sobering wake up call, Maguire said.
Dr Williams was the second person to die from COVID-19 in two days, taking the country's death toll to 24.