Prime Minister Malcolm Turnbull says the two are in addition to a woman, recovering in hospital from stab wounds, and another man who received stitches and is on his way back home.
"There are two other Australians, so that brings it to a total of four, about whom we have very real concerns, but at this stage we're not able to say anything more," he told reporters in Sydney on Monday.
Turnbull said Australian authorities were seeking further information about the circumstances of the two.
Three attackers rammed a hired van into pedestrians on London Bridge and stabbed others nearby on Saturday night in Britain's third major militant attack in recent months.
At least 48 people were injured before the militants were shot by police.
British Prime Minister Theresa May called for an overhaul of the strategy used to combat extremism following the attacks, including a demand for greater international regulation of the internet, saying big internet companies were partly responsible for providing extreme ideology the space to develop.
Turnbull reiterated her comments in Sydney, saying there needed to be greater global coooperation to tackle extremism online.
“There is too much tolerance of extremist material on social media and that, ultimately, requires cooperation from the big social media platforms, in particular, Facebook and Twitter.
