Australian intelligence agencies reportedly found China was responsible for a cyber attack on Federal Parliament earlier this year, but kept the finding secret to avoid souring trade relations with Beijing.

News agency Reuters reported on Monday the Australian Signals Directorate (ASD) found in March that China's Ministry of State Security was responsible for a "sophisticated" hack attack on MPs' emails and the networks of the Australian Labor Party, the Liberals and the Nationals.

It prompted fears at the time that if MPs' emails or data were stolen, they could be used to cause political interference during the May election campaign of the kind Russia perpetrated against the United States in the 2016 presidential campaign.

Reuters cited five sources who had declined to be identified because of the sensitivity of the issue.