The parliamentary computer of Australian premier Julia Gillard is suspected of being hacked along with those of the foreign minister and defence minister, with China under suspicion, a report said on Tuesday.
Sydney's Daily Telegraph said American intelligence officials tipped off the government that several thousand emails may have been accessed from the computers of at least 10 ministers.
As well as Gillard, they reportedly included Foreign Minister Kevin Rudd and Defence Minister Stephen Smith.
The paper said the espionage occurred over more than a month, beginning in February.
"Four separate government sources confirmed that they had been told Chinese intelligence agencies were among a list of foreign hackers that are under suspicion," it said.
Attorney-General Robert McClelland refused to confirm or deny the incident.
"It's the long standing practice of successive Australian governments not to comment on the operations of security and intelligence agencies," he said in a statement.
"Australia's security and intelligence agencies, as a matter of course, work closely and co-operatively with their international counterparts on cyber security.
"The Australian government takes the issue of cyber security very seriously and is constantly strengthening cyber security measures," he said.
The cyber-attacks are believed to have been on the Australian Parliament House email network, the less secure of two networks used by MPs.
Ministers use a departmental network for more high-security communications.