Top-secret US intelligence documents leaked by whistleblower Edward Snowden have revealed details of a key signals intelligence program used by the Australian intelligence community to harvest internet and telecommunications traffic across the Asia-Pacific region.

The system known as X-Keyscore allows the US National Security Agency and international partners including Australia to monitor ''nearly everything a typical user does on the internet'', according to the leaked documents published by Britain's Guardian newspaper.

According to classified intelligence training materials, X-Keyscore allows the NSA and its allied partners to comprehensively monitor the emails, web browsing, internet searches and social media use of targets.

This includes ''real-time target activity [tipping]'' and a ''rolling buffer of three days of all unfiltered data'' with the ''full take'' stored at collection facilities - enabling analysts to retrospectively access the communications of newly identified targets.

Significantly, all the secret documents are classified as available to personnel from ''5-eyes'' intelligence partners: the US, UK, Canada, Australia and New Zealand.