Police said officers were called to Port Botany at about 6.50 pm yesterday amid an “unauthorised protest”.
Many demonstrators were waving Palestinian flags and calling for a ceasefire in Gaza.
9News witnessed a number of clashes between police and protesters, with the riot squad attending the scene.
Police said the demonstrators were directed to move from Penrhyn Road, where they were allegedly blocking the roadway and access to the port.
A total of 19 people were arrested after allegedly refusing to move, and charged with obstructing the road, ignoring a move-along order and disrupting a major facility.
They will appear in court on May 8.
The rest of the demonstrators were removed from the road, police said, with “a small group” gathering in a nearby park before leaving.