Activists met at a Hamilton hotel on Saturday to form a coalition against the plan.

There is concern the plan will damage marine ecosystems and beaches and hamper moves towards renewable energy.

Advent Energy, through its subsidiary company Asset Energy, plans to begin exploratory drilling this year for natural gas 27 kilometres to 55 kilometres off Newcastle.

Lake Macquarie councillor Phillipa Parsons, who called Saturday's meeting, created a Facebook page yesterday called Hands off Our Coast.

"The plan has huge potential to inflict damage to the marine environment and tourism and commercial industries such as fishing, cruise ships and whale-watching," Cr Parsons said.

There is concern that the drilling plan, which needs state and federal approval, lacks transparency and scrutiny.

The Newcastle Herald reported on Thursday that NSW Primary Industries Minister Steve Whan said Advent's environment plan for the proposal did not have to be made public under federal law.

Cr Parsons said it was "secret mining business they don't want people to know about".

Advent said extracting gas would be good for the environment because it produced less carbon dioxide emissions than coal.

Cr Parsons said governments were wrong to continue to pursue gas exploration and extraction because it was a fossil fuel.

"They are wasting precious time and opportunity to develop clean, renewable energy," she said.