German police deployed a water cannon and pepper spray to disperse around 500 protesters in Hamburg, ahead of the Group of 20 (G20) Summit this weekend, where advocacy groups say global leaders will continue to support a flawed model for creating a more just world.

Some activists gathered to march on a main street of the port city just before midnight on Tuesday, while hundreds had pitched tents along the Elbe river. Tuesday's events follow weekend demonstrations that brought at least 10,000 peaceful protesters to Hamburg's streets and waterways. Tens of thousands more anti-globalization protesters are expected to flood Hamburg over the weekend, as the summit kicks off.

Friday, representatives of the world's 20 largest economies—19 countries and the European Union—will meet in Hamburg for the two-day summit hosted by German Chancellor Angela Merkel. Attendees will include U.S. President Donald Trump, Russian President Vladimir Putin, and Turkish President Recep Tayyip Erdoğan.

At least 30 groups have registered to demonstrate in Hamburg this week, organizing to challenge the G20's agenda and the policies touted by nationalists like Trump and Putin, and the liberal European leaders alike.

"The model itself is broken," said Nick Dearden of Global Justice Now. "This G20 has been hailed as a showdown between the responsible free trade leaders of Europe and the dangerous populist strongmen like Trump, Putin, and Erdogan. But it's exactly because of these free market policies which have so badly undermined democracy and trust in political institutions that an extremist like Trump is now in the White House. We need a new model to undermine the racism and thuggery of Trump and his ilk—one that values human life before the profits of the superrich.”

Germany will have up to 20,000 police officers on duty during the summit, utilizing technology that includes a fleet of water cannons, and underwater and aerial drones.

"You can be certain that you will see all of the equipment that German police have here in Hamburg," the city's police security team leader told The Associated Press. Photos and videos of police using "WaWe10" water cannons on demonstrators Tuesday night have circulated social media:

Hamburg police chief Ralf Martin Meyers expressed concerns about violence to the Guardian: "There is evidence that the acts of violence around the G20 summit that we had expected and feared will take place." German officials have specifically targeted their concerns at the anarchist "Welcome to Hell" demonstration. However, so far the protests have been peaceful.

Even so, German officials have set up a 38-square-kilometer (about 15-square-mile) "no-protest zone" around the airport where foreign leaders will arrive and the convention center where the summit will take place.

Many groups planning actions for this week, including Greenpeace, have opposed this decision and have emphasized the importance of peaceful demonstrations. Greenpeace International's executive director Jennifer Morgan told AP: "We're looking for the G20, and if that's not possible, then the G19, to go forward with implementing the Paris agreement and maybe doing even more," adding: "Greenpeace stands for nonviolent direct action—we have peace in our name—and it would be a shame if violence moved the message away from what the G20 should be doing on climate and other issues."