He congratulated and thanked about 100 volunteers during the Mayor's Morning Tea held on International Volunteer Day at the Dunedin Public Library yesterday.
Mr Cull said in his capacity as the mayor and a city councillor he had become aware of the "enormous'' amount of voluntary work undertaken in the wider community.
"I shudder to think what our communities would be like were it not for the efforts of people like you,'' he told the crowd.
Mr Cull said voluntary work ranged from random acts of kindness to organised campaigns and benefited a wide variety of people, including the volunteers themselves.
It was estimated volunteers in New Zealand did the work of about 134,000 fulltime equivalent positions, he said.
Mr Cull was asked to speak at the function by Volunteering Otago, which organised the morning tea.
Manager Anna Clere was delighted about 100 people attended, but said the number represented "the tiniest tip of the iceberg'' in terms of all volunteers throughout the region.