Hundreds of protesters have gathered outside a major arms expo in Sydney .

The protest against the Indo Pacific International Maritime Exposition kicked off at about 6.30am in Tumbalong Park, Darling Harbour, across from the International Convention Centre where the event is being held.

The three-day expo is the "premier commercial maritime and naval defence exposition, connecting Australian and international defence, industry, government, academia and technology leaders, in the national interest", according to the NSW government.

A heavy police presence is also at the scene, including mounted officers, to prevent protesters blocking attendees from entering the building.

Multiple arrests have been made already.

"We're here to peacefully protest against a convention of war crim

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