Crossbenchers have raised concerns in Parliament that the Federal Government is promoting the controversial Adani mega-mine to foreign governments in an effort to secure funding for the project.

The Turnbull Government said it was not advocating on behalf of the Indian company, but has confirmed it has written to the Chinese Government to assure it the Carmichael coal mine has been approved.

Senate crossbenchers questioned officials from the Department of Foreign Affairs and Trade (DFAT) in Senate Estimates after a Freedom of Information request to DFAT for documents relating to requests for foreign government financing for the controversial multi-billion-dollar mine and rail project.

Attorney-General George Brandis did not confirm whether that had occurred but said the Government had made representations to dispel misinformation about the Carmichael mine.

"The Australian Government has written to the Government of China to confirm the project has received all necessary Queensland state government and Australian government environmental and mining approvals," he said.

Senator Brandis said he did not know whether the letter was sent on request by Adani, but department secretary Frances Adamson said she expected Adani did ask for the letter to be sent.

"I would expect so because a letter setting out the status of the project would have been generated as a result of a perceived need for that I expect," Ms Adamson said.

Following a lunch adjournment, Ms Adamson revealed more details about the letter.

"The letter was written by the Minister for Trade, Tourism and Investment and by the Deputy Prime Minister," she said.

"It was a statement of fact where the project is up to and a statement of endorsement of support by the Australian Government."

Letter not 'an approach to a foreign agency'

Tasmanian senator Jacqui Lambie asked why it was necessary to inform the Chinese Government about the project.

"Has this got to do with money being lent from the Chinese?" she asked.

Senator Brandis took the question on notice. He said it was not "an approach to a foreign agency", rather it set out the facts of the project.

DFAT officials have told Senate estimates it was not the department's role to seek finance for the Adani project.

Responding to the delay in the FOI request, Ms Adamson said the fact it had captured several hundred pages of documents did not mean official approaches had been happening.

"The fact that there are a significant number of documents that we've identified for review should not be read to imply that there's a significant amount of departmental activity," she said.

"My understanding is there has not been a significant amount of activity."

Greens leader Richard Di Natale asked whether, "the representation that's been made has been limited to advocacy for the project but there has been no representation made with regards to obtaining foreign finance?"

Ms Adamson replied: "It's not been DFAT's role to seek foreign finance for the project."