Ten people were arrested and two officers were injured as police declared two out-of-control gatherings in Perth's CBD overnight, in what was a violent end to Australia Day in the city.
Police said they were called to Wellington Street outside Perth train station about 10pm on Thursday to disperse a crowd of about 150 people, after reports of two large groups of people fighting.
Police said several people threw rocks and bottles at officers.
WA Police said the safety of the public and officers was put at risk, with extra officers sent to the scene, forming lines to separate the groups and arrest those responsible.
Marked and unmarked patrol cars with lights and sirens blaring were seen racing to the CBD through red traffic lights.
Assistant Commissioner Brad Royce said the trouble was sparked by a clash at Perth train station.
"The initial violence came about from an interaction between transit guards doing their jobs, and people at the train station," he said.
"There was pretty poor behaviour by members of the crowd that probably weren't involved in the first instant that saw it as an opportunity to act out."
More than 1,000 people gathered in that same location at Forrest Place hours earlier for the city's Invasion Day rally.
More trouble flares in East Perth
Three arrests were made in the early hours of the morning as police declared another out-of-control gathering about 1:20am at Moore Street, near the McIver train station in East Perth.
Police said a number of offenders armed themselves with projectiles including broken paving bricks, while one person was carrying a tomahawk.
A WA Police spokesperson said objects were thrown at police as they dispersed the crowd.
"There were three arrests and two of our officers were injured, luckily not seriously. Both are back out and about," Assistant Commissioner Royce said.
"One had a dislocated shoulder which righted itself, and then one had some minor facial injuries from a scuffle, but both are okay."
Police earlier said the two injured officers had been taken to hospital.
Violence not being linked to Australia Day
Assistant Commissioner Royce said nothing indicated the violence was related to anti-Australia Day anger.
"There was nothing to suggest, that I know of, that that was the issue at this stage," he told ABC Radio Perth.
"What started off as a couple of small groups fighting quickly got out of control once we got involved, and [people] started throwing paver bricks and bottles and other pieces of equipment they could find at officers."
"This was between two groups before we got there.
"Personal issues aside between groups, we step in because the rest of the community don't need to be involved and have that going on."
Police 'careful' over using new laws
Assistant Commissioner Royce said footage of the incidents would have to be reviewed further before any charges and other consequences could be acted out.
WA Police were given powers in December to exclude people from designated protected entertainment precincts for up to six months for anti-social and threatening behaviour.
"We're reviewing footage, but they've got to be a sufficient level to warrant that. So disorderly behaviour, things like that, don't really fall into that space at the moment," Assistant Commissioner Royce said.
"We want to be careful to make sure if we are going to remove someone from a precinct for up to six months, there's a pretty good reason."
In a statement, Police Minister Paul Papalia condemned violence against police.
"What happened in the CBD of Perth last night was totally unacceptable unlawful behaviour. Police officers should not have to go to work and have rocks and bricks thrown at them, it will not be tolerated anywhere in Western Australia," he said.
Thousands watch scaled-down fireworks
The City of Perth estimates about 52,000 people gathered earlier in Langley Park to watch a scaled-down Australia Day fireworks event.
While the previous Skyworks event was replaced with a smaller fireworks display, an accompanying drone light show that formed 3D shapes above the Swan River drew gasps from the crowd.
The City of Perth said it was changing the feel of the event in light of changing community attitudes towards holding celebrations on January 26.
While many in the crowd wanted to continue the tradition on January 26, others thought it was no longer appropriate due to its links to the country's colonial past.
Change of date 'inevitable': Lord Mayor
Lord Mayor Basil Zempilas said the violence was "totally unrelated" to Australia Day celebrations in the city.
"They were totally separate crowds, totally separate events," he said.
"The people that went to Langley Park were magnificent. They enjoyed a great show, they had a great night, they celebrated and marked Australia Day respectfully."
However, he urged Prime Minister Anthony Albanese to "get on" with changing the date of Australia Day if that was his intention.
"My view is that the Prime Minister has put local councils — and therefore the community — in a very difficult position by allowing some councils to have their Australia Day events a few days before Australia Day, or a few days after," he said.
"That has, by its very nature, clearly contributed to division.
"If we're going to change the date, then change it and I'll support whatever date Australia Day is, as mandated by the prime minister and the federal parliament, we will embrace it, we will celebrate it.
"But it's not my job as Lord Mayor to change the date. It is the job of the Prime Minister to lead this conversation.
"And it's created what I think is division in our community as we wait for what I consider to be almost an inevitable change of the date for Australia Day.
"So my message to the prime minister is if you're going to change the date, if that's what you think is best, then get on and do it."
Mr Zempilas suggested Prime Minister Anthony Albanese was potentially pushing for a change to the date by "stealth" by forcing councils to make the hard decisions around the issue.
"It's been perhaps on the agenda by stealth...[by] asking councils to do that groundwork to get the nation ready for a change of date."
He said the violent clashes in the CBD would not deter the City of Perth from holding events.
"We're not going to put barriers up around the city, we're not going to get scared, we're not going to run away, we're going to continue to stage large scale family events that get enjoyed by majority of our well-meaning population," he told ABC Radio Perth.
