More than a dozen people are under arrest and at least one police officer has been left bloodied after violent clashes outside a naval weapons expo.

Hundreds gathered 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.

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.

Ten people were arrested, including two soon released without charge, as police struggled to hold back the crowd as it surged about 8am.

A mid-morning lull was followed by further clashes and more arrests as Chief of Navy Vice-Admiral Mark Hammond prepared to open the expo about 11am.

Four people were seen on the ground during the later flare-up while an officer was seen 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.

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.”

Multiple skirmishes led to more than a dozen arrests. Photo: AAP

Much of the protest focused on the NSW government’s role in hosting and sponsoring the expo amid the conflict in Gaza.

Exhibitors include Israeli weapons manufacturers and other firms supplying that nation’s military.

“Chris Minns, blood on your hands,” attendees chanted, referring to the NSW premier.

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.

“It’s a maritime conference relating to the Navy.”

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.”

The protest comes a year after similar scenes in Melbourne, when thousands of demonstrators clashed with police and attendees at a major defence and weapons expo.

Protesters lit multiple fires near the expo, blocked traffic and climbed on top of a truck.

–AAP