The Queensland government's secret plan to build a publicly-funded harbour to help mining companies ship coal through the Great Barrier Reef wasn't included in a crucial report to the federal environment minister, a conservation group says.

Documents obtained by the North Queensland Conservation Council revealed the "hidden" plans for the tugboat harbour that weren't included in an Environmental Impact Statement provided to Greg Hunt by the Queensland Department of State Development, the group and 350.org say.

"The EIS is incomplete, is not an accurate assessment of the Abbot Point project and its likely impacts, and is likely to dramatically understate those impacts," NQCC campaigner Jeremy Tager said on Thursday.

"Mr Hunt now needs to step in and immediately hit pause on the approvals process for Abbot Point, require a full and complete environmental assessment from the Queensland government, and investigate whether the Queensland government has engaged in false and misleading practice."

The documents reveal the harbour would be paid for by the government at an estimated cost to the public of $90-$125 million, NQCC said.

"It appears that this project amounts to a backdoor subsidy for the likes of Adani," Mr Tager said.

"(A) taxpayer-funded largesse for a foreign coal billionaire at a time when Queensland is in a state of budget emergency, when the reef is in peril, and when the Queensland government is pretending that it cares about climate change."

Several different plans for the harbour were included in the documents, including a "preferred option" previously rejected due to possible impacts on endangered turtle nesting sites.

Moira Williams from 350.org also said the decision to approve Indian mining giant Adani's Abbot Point project should be halted.

"Just days after a global climate deal was reached in Paris, we discover that the Queensland government has been making secret plans to help expand coal exports here in Australia," she said.

Projected coal volumes mean the port would need to be operational by 2021, Mr Tager said.