Key federal crossbenchers have questioned senior government bureaucrats about possible secret approaches to foreign agencies for financial support for Adani's controversial Carmichael coal mine.

Key points: Senator Xenophon wants to know what representations the Government made to foreign agencies

Senator Xenophon wants to know what representations the Government made to foreign agencies Australian embassies overseas were searched for documents

Australian embassies overseas were searched for documents An FOI request on the issue has "captured several hundred pages of documents"

The questions have been sparked by a Freedom of Information request to the Department of Foreign Affairs and Trade (DFAT) for documents relating to requests for foreign government financing for the controversial multi-billion-dollar mine and rail project.

In response, DFAT asked for more time to respond as the request had "captured several hundred pages of documents".

Senator Nick Xenophon said he would be demanding clarification from DFAT officials at Senate Estimates today about what representations the Federal Government has made to foreign agencies.

"It is not the role of the Australian Government or its diplomatic missions to be involved as finance brokers for a very controversial project like this," he said.

"There needs to be an open and transparent process."

Greens leader Richard Di Natale said the Federal Government must tell the public if any representations have been made to international finance agencies about funding Adani's projects.

"DFAT, the Foreign Minister, the Trade Minister, should immediately come clean with what sort of secret deals are going on between some of these finance companies, international companies, and the Australian Government," he said.

The FOI request was lodged in August by The Australia Institute, which asked for all "correspondence and cables" relating to requests for foreign government financing of Adani's projects.

Specifically, it asked DFAT for any documents that "include or refer to any formal representations made by any Australian Government minister or official requesting or recommending consideration of financial contributions towards or involvement in these projects" from foreign government agencies in 2017.

These included "export-import banks or credit agencies, or multi-lateral financing agencies, or foreign private sector financiers".

Embassies searched for documents

Sorry, this video has expired Giant Indian conglomerate Adani has a complex network of companies ultimately owned in the Cayman Islands

In response, DFAT sought an extension, "due to complexity and volume as your request has captured several hundred pages of documents".

The department also revealed three Australian embassies overseas were searched for documents.

"The Australian Government appears to be helping Adani secure financial assistance and support from overseas," said The Australia Institute's executive director Ben Oquist.

"The fact that the department has said there are several hundreds of pages relating to multiple countries and from departments in Australia … suggests there is a lot of work going on."

DFAT deferred comment to the Trade Minister Steven Ciobo.

Mr Ciobo did not answer questions relating to whether any representations had been made to foreign agencies about financing or involvement in Adani's project, but he confirmed an FOI request was currently being considered.

"A large number of documents were potentially captured under the FOI request," he said.

"Any documents released to the FOI applicant will also be placed on the department's public FOI disclosure log in due course."

Foreign Minister Julie Bishop declined to comment.

DFAT has applied to the Office of the Australian Information Commissioner for a second extension before deciding whether it will release any documents.

'Hit a road block'

Senator Xenophon said he was not "implacably opposed to Adani", but wants transparency from DFAT.

"I am very concerned that this FOI request appears to have hit a road block because it may well contain embarrassing information … it is important that these documents be released as a matter of urgency," he said.

Senator Nick Xenophon says "there needs to be an open and transparent process" regarding the Adani mine. ( ABC News/Adam Kennedy )

Senator Di Natale said he would also be asking officials from the Department of Foreign Affairs and Trade about the matter at Senate Estimates today.

"I want the department to make it absolutely clear if any guarantees, if any deal has been done with some of these (international) finance companies," he said.

"I want to make it absolutely clear that the Australian taxpayer … will be looked after if this project falls over and the Australian Government has entered into some sort of arrangement with an international company to prop it up."

Australia's big four banks have all ruled out providing finance to Adani.

Adani is seeking a $1 billion federal loan from the Northern Australia Infrastructure Facility for the rail line linking the Carmichael coal mine to the port of Abbot Point, which it also owns.