Australian secret service officers on Thursday secured thousands of classified documents that were sold with two secondhand filing cabinets.

Australian Security Intelligence Organization officials entered Australian Broadcasting Corp. bureaus in Parliament House in the capital of Canberra and in the city Brisbane with safes in the early morning hours, the state-owned broadcaster said.

Both the secret service, known and ASIO, and the ABC have access to the safes that remain on ABC premises, said reporter Matthew Doran, who was in the Parliament House bureau when the safes arrived.

The ABC revealed on Wednesday that it had thousands of Cabinet documents that had been found in two filing cabinets sold from a Canberra secondhand furniture store.

The cabinets were sold at a discount price because they were locked and no one could find keys, ABC reported.

The ABC has not identified the buyer who removed the locks with a drill and found thousands of mostly classified papers spanning almost a decade and four prime ministers, the most recent being Tony Abbott. Abbott was replaced in 2015 by the current Prime Minister Malcolm Turnbull.

The Department of Prime Minister and Cabinet on Wednesday initiated an urgent investigation into the disposal of the filing cabinets.

ABC Director of News Gaven Morris said the documents were secured as a result of negotiations between lawyers for the ABC and the prime minister's department.

"We worked with the government to ensure that as quickly and as safely as we could that these documents could be secure, that there was no question of there being any further threat to national security," Morris said.

He added: "The documents are now secure on ABC premises, we want to ensure that the government is perfectly satisfied that there is no threat of them getting into the wrong hands or anything else."

"But equally we want to ensure that the editorial principles of the ABC are maintained as well and we continue to work with the government on what next to do," he said.

ASIO did not immediately respond to emailed questions on Thursday.

Turnbull said police were involved in his department's investigation.

"It's a dreadful failure of responsibility," Turnbull told Radio MMM Darling Downs. "The people responsible will pay a heavy price, I can assure you."

The papers' classifications include "top secret," "sensitive," ''Australian eyes only," and "Cabinet-in-confidence," the ABC reports.

The ABC has not said when the documents were found. But it has used them in recent weeks to report stories that have been embarrassing to the former administrations of Prime Minister Kevin Rudd and Abbott as well as a number of serving lawmakers.

Rudd, who has retired from politics, announced on Thursday that he was taking legal action against the ABC over one report.

The ABC said it had chosen not to report some documents on national security grounds.

Australian Cabinet documents are usually kept secret for 20 years, before they are made public in a heavily redacted form.