The protest at Port Botany in Sydney's east was held on Sunday night with Maritime Union of Australia (MUA) activists saying it was a "peaceful community assembly" at one of the terminals.

Hundreds of protesters, including federal Greens senator Mehreen Faruqi, took part, demanding state and federal governments prohibit Israeli company ZIM from entering Australian ports and implement broader sanctions on Israel.

The group says the Israeli company is complicit in the war in Gaza.

The union said 15 minutes after the protest began, police moved in and began assaulting and arresting demonstrators, including MUA branch secretary Paul Keating, organiser Shane Reside and other delegates.

Video of the protests show scuffles between protesters positioned on a roadway and a cordon of officers.

NSW Police confirmed 19 people were arrested and charged.

Officers responded to the "unauthorised protest" at Port Botany at 6.50pm before the group moved to Penrhyn Rd, blocking access to the port, police said in a statement.

"The crowd was directed to move from the roadway and given some time to do so," the statement said.

"A number did not comply and were arrested for disobeying police direction."

Senator Faruqi said police aggression against protesters was an attack on democracy.

"People have the right to protest and demand change where governments are utterly failing," she said.

"I stand in solidarity with every person who is risking their safety and freedom to practice their democratic right to protest."

But Premier Chris Minns said police had a responsibility to keep order in NSW and that protesters had "deliberately ignored" a lawful directive.

"There's major implications when you try and disrupt one of the arteries of our economic growth that is NSW ports," he told reporters on Monday.

"I think ultimately a lot of these protesters are going to do more damage to their cause than strengthen it as a result of disrupting tens of thousands of people through these activities."

Mr Minns backed the police response and said he did not believe officers had been heavy-handed.

"NSW Police do an amazing job, it's extremely difficult to always insert them in these points of contention - sometimes violence, sometimes aggro from protesters - and they keep their heads, they keep their cool and they keep the NSW public safe," he said.

The 19 people arrested were charged with obstructing a driver or pedestrian's path, failing to comply with a move-along direction and remaining near a major facility causing a serious disruption.

They will appear in court on May 8.

Australian Associated Press