About at 12:15 a.m. local time two groups of fans clashed just outside the main tennis arena, which caused dozens of police moved into the area to break up the fight.

"The Serbs were chanting against the Croatians, the Croatians were chanting against the Serbs and it all got out of hand, mate," an anonymous witness said.

So far there were no injuries or arrests reported.

"About 150 people were ejected from the venue," Victoria Police spokeswoman Katherine Jess said, adding "they were mostly Serbians ejected as they were upsetting the Croatians."

Earlier, about 200 fans congregated at Federation Square about 10 a.m. local time, chanting and letting off flares as they made their way to the venue, she said.

"Police are now meeting with Tennis Australia officials to work out the next move," Jess added.