Australian security intelligence officers have secured thousands of top secret documents found in two filing cabinets sold at a second-hand store.

An urgent investigation has been launched after the documents were found in the locked cabinets purchased at a furniture store in Canberra.

The Australia Broadcasting Corporation (ABC) reported on the embarrassing discovery after obtaining the documents.

The documents contained classified information. Credit: AuBC

The cabinets were sold at a furniture store for a discounted price because no one could find keys to open them, the national broadcaster reported.

ABC said the buyer, who has not been identified, found mostly classified papers spanning nearly a decade and four prime ministers, most recently Tony Abbott.

Abbott was Prime Minister of Australia for two years from 2013-2015, the files also reportedly cover his predecessor Julia Gillard's government.

Australian Cabinet documents are usually kept classified for 20 years, before being made public in redacted form.

Some of the documents were reportedly related to Tony Abbott's government among others. Credit: AP

The government has ordered a review into how the cabinets were disposed with the files in them.

Meanwhile, former prime minister Kevin Rudd has launched legal action against ABC after it published details from one of the document related to his government’s home insulation scheme.

Mr Rudd said the report which alleged he ignored warnings on risks to the safety of installers was "a lie".

Australian secret service officers have now secured the classified documents after negotiations between the prime minister's department and ABC.

ABC Director of News Gaven Morris said: "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."