The mining industry was left in no doubt that Dunedin's council is not welcoming it here and is on notice to figure climate change strategies into their operations.

As the Mining Forum at the Dunedin Town Hall got off to a belated start this morning, the close to 300 delegates inside could hear the faint chanting of more than 100 protesters outside.

Delegates had been forced to arrive at 6.30am for an 8am start, with several still stranded outside at 8.30am, as protesters shadowed and rushed myriad entrances into the hall and council building, with several physical confrontations taking place.

Two chief executives of gold and coal companies had coal thrown at their feet outside.

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When Dunedin Mayor Dave Cull spoke he grabbed the immediate attention of the delegates.

"So to be clear, if you're promoting fossil fuel exploration, extraction and exploitation and especially its expansion, then understand you are at odds with this community and my council that represents it," he said.

He acknowledged Dunedin was built on gold, from the rushes of the 1860s and remained important today, given Ocean Gold's Macraes operation in East Otago contributed $80 million in local gross domestic product (GDP) and 500 jobs.

Between Macraes and Waihi in the central North Island, Oceana produces about 98 per cent of the country's gold annually.

"And I acknowledge that over the years we were a city reliant on a good deal of fossil fuel energy.

"Unfortunately we still are," he said.

However, Cull made it abundantly clear to the delegates the community's attitude to fossil fuels had changed since gold was discovered more than 150 years ago.

"We don't have any right to trade in our children's and grandchildren's futures just to make a quick dollar now," he said to the silent audience.

He said the protestors outside, "however impolite and disrespectful" were expressing the "overwhelming view of this community and my council".

Cull said while the forum was discussing traditional mining areas such as coal, he hoped it would be "genuinely discussing''' climate change and sustainability, so that people could have informed debate.

"However, I think you will now be under no illusions about which side of the debate I and this city have landed on," Cull said.

He said in the medium to long term, sea level rise, prompting rising groundwater, would further increase the risk and potential impact to low-lying areas like South Dunedin, where there was 2700 homers less than 50cm above the spring high tide mark, which was more than in any other city of New Zealand.

"A higher frequency and intensity of rain events poses the most immediate risk and potential impact here.

"We've had several major flooding events in Dunedin in recent years with massive financial, physical and emotional impacts," he said.

He said "incredibly hard decisions" were now having to made in Dunedin about how to protect communities from flooding, coastal erosion and sea level rise, because of decades of inaction by governments; local, central and international, and also the fossil fuel industry.

He said there had been an undermining of healthy public policy by the powerful influence of vested interests, the fossil fuel industry.

"But that harmful influence can no longer be tolerated."

That is why the Dunedin City Council and University of Otago divested their shares from companies associated with fossil fuel exploration, extraction and exploitation, he said.

"I suggest the beneficiaries of business and industry you and your shareholders - are responsible to the communities your industries work in and affect," Cull said.

Meanwhile, Rory McCarthy, speaking at the public forum at the start of today's Dunedin City Council meeting, urged councillors to declare a climate emergency in Dunedin.

But he also urged the council to go further, from pushing to end the city's reliance on fossil fuels and create a Citizens' Assembly, to promoting public education on initiatives like car-pooling and solar panels.

"This isn't a game or a statistic. This is our very lives and the future of our children."