Hundreds rallied at Sydney's Darling Harbour on Tuesday to protest the Indo Pacific International Maritime Exposition, a three-day event billed as the nation's premier commercial maritime and naval defence forum.
Exhibitors include Israeli weapons manufacturers and other firms supplying that nation's military.
An attempted blockade of the biennial event, organised by the Palestine Action Group, escalated tensions with police as the conflict ebbed and flowed throughout the five-hour protest.
Multiple skirmishes broke out where pepper spray and other police force was used, with many protesters washing their eyes after clashing with authorities.
Thirteen people were arrested, including two who were soon released without charge.
Police struggled to hold back the crowd as it surged about 8am before further clashes and more arrests about 11am as delegates inside prepared to hear from Chief of Navy Vice Admiral Mark Hammond.
Four people were seen on the ground during the later flare-up while an officer was left with blood on his face.
Riot police were deployed, protecting an entrance to the expo at the International Convention Centre Sydney, about 100 metres from where demonstrators had gathered.
Protesters marched to the nearby Sydney Town Hall before dispersing, police said.
Protest organiser Josh Lees said demonstrators wanted to blockade the convention but they were met with strong police force.
"We were just trying to assemble near the IMAX, which is what we said we're going to do, and the police attacked us immediately with horses, pepper spray," he told reporters.
"They made some arrests there. They injured some people there, and forced us back into this park."
Much of the protest focused on the NSW government's role in hosting and sponsoring the expo amid the conflict in Gaza.
"Chris Minns, blood on your hands," attendees chanted, referring to the NSW premier.
Addressing a report that export controls were tightened on Tuesday, Defence Industry Minister Pat Conroy said the only export licences being approved related to maintenance, upgrades or manufacture of Australian Defence Force equipment.
"We haven't supplied ammunition or weapons to Israel over the last five years," he told reporters.
"The only export licences that are being approved right now (are) for ADF equipment that is going to Israel for either repair or upgrade or manufacture to come to back to Australia."
Government figures have consistently denied that Australia exports weapons to Israel, although local companies have produced parts for F-35 jets used in the two-year bombing campaign in Gaza.
Mr Minns told ABC radio he was unaware of the circumstances surrounding the protests and had no input into decisions regarding Australia's relationships with foreign countries or arms manufacturers.
"They're not selling nuclear weapons down at Darling Harbour this weekend," he said.
The conference, focused on strength at sea, was important for a nation reliant on maritime trade and submarine cables, the chief of Navy told attendees.
"The reality we face is that you do not need to invade Australia to defeat Australia," Vice Admiral Hammond said.
"To safeguard our nation's security and prosperity at home, we must be strong at sea."
Protesters have vowed to rally each day of the expo.
The violence mimics scenes in Melbourne in 2024 when thousands of demonstrators clashed with police and attendees at a major defence and weapons expo.
Protesters lit multiple fires near the convention centre, blocked traffic and climbed on top of a truck.
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