Tennis Australia banned Russian and Belarusian flags from the event at Melbourne Park earlier this month, after a spectator was reported to security for displaying one during a match between Ukraine's Kateryna Baindl and Russian Kamilla Rakhimova.
Russian and Belarusian players have not been able to play under their countries' flags since Vladimir Putin's regime launched an invasion of Ukraine last February.
On Wednesday, spectators were seen displaying a Russian flag during Andrey Rublev's quarter-final defeat against Novak Djokovic, while one man appeared to be wearing a t-shirt adorned with the letter 'Z' – used as a pro-war symbol in the country.
The man was seen in conversation with an Australian Open official at Rod Laver Arena, while social media footage later showed a flag featuring Putin's face being waved outside the venue.
A widely reported statement from Tennis Australia read: "Four people in the crowd leaving the stadium revealed inappropriate flags and symbols and threatened security guards.
"Victoria Police intervened and are continuing to question them.
"The comfort and safety of everyone is our priority and we work closely with security and authorities."