HAMBURG, Germany -- U.S. President Donald Trump and other leaders of the Group of 20 top industrial and developing countries arrived Thursday in Hamburg as police in Germany's second-biggest city braced themselves for a major protest by anti-globalization activists.

German Chancellor Angela Merkel said she hoped the G-20 leaders meeting today and Saturday would be able to find "compromises and answers" on a wide range of issues.

Merkel said leaders would address regulating financial markets, fighting terrorism and pandemics and combating climate change, among other issues. She said "free, rule-based and fair trade" will be an important issue.

"You can imagine that there will be discussions that will not be easy," she said. "Globalization can be a win-win situation. It must not always be that there are winners and losers."

The northern German port city boosted its police force with reinforcements from around the country for the summit and had 20,000 officers on hand to patrol Hamburg's streets, skies and waterways.

More than 100,000 protesters are expected in the city for the summit, with some 8,000 considered part of Europe's violent left-wing scene, according to police.

Ahead of the summit, a Thursday evening demonstration was planned, which organizers titled "G-20: Welcome to Hell."

While protests so far had been largely calm, city police chief Ralf Martin Meyer told ZDF television: "We are skeptical as to whether this evening and tonight will remain peaceful."

Demonstrators promised massive protests against Trump, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan, three of the more controversial guests at the summit.

A large sign in a shop window near the summit venue featured pictures of the three with the slogan: "We don't want that!"

A large banner hanging from a building overlooking the congress center where the leaders will meet said: "G20 Members: Respect the rule of law!"

Canadian Prime Minister Justin Trudeau, Chinese President Xi Jinping and South African President Jacob Zuma were among the first to arrive Thursday, while Trump joined in the late afternoon, flying in from a stop in Warsaw.

For the anti-globalization protest Thursday night, organizers said they were "calling on the world to make Hamburg a focal point of the resistance against the old and new capitalist authorities."

Overnight, 10 cars were set ablaze outside a Hamburg Porsche dealership, which police are investigating as possibly summit-related.

Many other groups are calling for peaceful protests and are pushing the G-20 leaders for action on climate change, to address economic disparities in the world and a wide array of other issues.

Some are calling for the dissolution of the G-20 itself so the United Nations becomes the platform for such discussions.

In the wake of Trump's recent decision to pull out of the Paris deal fighting climate change, the battle against global warming promises to feature prominently in discussions at the summit.

Merkel has rejected calls from some to push for a strong "G-19" statement -- without the U.S. -- on climate change. That is something Zhu Guangyao, a Chinese deputy finance minister, told reporters Thursday that Beijing also did not support.

"The policies produced by the G-20 should be by the consensus of all member states," he said. "No one should be excluded."

Still, he added, "China will firmly promote its policies taking more measures against climate change."