HAMBURG, Germany (AP) — German Chancellor Angela Merkel told leaders of the Group of 20 economic powers Friday that millions of people are hoping they can help solve the world's problems, and warned them that they must be prepared to make compromises.

As the leaders discussed terrorism, trade and climate change, protests against their gathering continued in various parts of Hamburg. Anti-globalization activists set dozens of cars ablaze and protesters tried unsuccessfully to block leaders' delegations from getting to the downtown convention center where the summit is being held.

Police ordered in several hundred more officers from across the country on Friday.

Inside the security cordon, Merkel's prospects of finding common ground issues such as climate change and multilateral trade looked uncertain at President Donald Trump's first G-20 summit. Trump's "America First" rhetoric and decision to withdraw from the Paris accord against climate change have caused widespread concern in Europe and beyond.

"There are of course millions of people following us with their concerns, their fears and their needs, who hope that we can make a contribution to solving the problems," Merkel told fellow leaders at the start of a working lunch at which they were to discuss global growth and trade.

"I am absolutely sure that everyone will make an effort to achieve good results," she added.

"We all know the big global challenges, and we know that time is pressing," Merkel said. "So solutions can only be found if we are prepared to compromise ... without, and I say this clearly, bending ourselves too much out of shape. We can of course also name differences."

Merkel noted that the countries at the summit represent two-thirds of the world population, four-fifths of the globe's gross domestic product and three-quarters of world trade.

The G-20 comprises Argentina, Australia, Brazil, China, Germany, France, Britain, India, Indonesia, Italy, Japan, Canada, South Korea, Mexico, Russia, Saudi Arabia, South Africa, Turkey, the United States and the European Union.

Also attending the summit are the Netherlands, Norway, Spain, Guinea, Senegal, Singapore and Vietnam.

Before the summit, the leaders of China, India, Russia, Brazil and South Africa met and called for a more open global economy.

In a statement following their meeting, the so-called BRICS nations voiced support for a "rules-based, transparent, non-discriminatory, open and inclusive multilateral trading system" and emphasized the need for increasing "the voice and representation" of emerging markets and developing countries in global economic and financial institutions.

Speaking at the meeting, Russian President Vladimir Putin spoke against global trade restrictions, saying that financial sanctions on a political pretext hurt mutual confidence and damage the global economy — an apparent reference to Western sanctions against Russia.

The BRICS leaders also urged the international community to work jointly to implement the Paris climate agreement.

The summit, at which Trump was holding his first meeting with Putin, follows skirmishes Thursday evening between police and protesters at a demonstration in Germany's second-biggest city that was expected to be the largest flashpoint around the summit.

Police said that at least 111 officers were hurt during those clashes, one of whom had to be taken to a hospital with an eye injury after a firework exploded in front of him. Twenty-nine people were arrested and another 15 temporarily detained.

On Friday, there were further incidents but nothing as intense as Thursday's skirmishes.

Dozens of officers built moving lines in different parts of Hamburg and used water cannons to force away protesters from streets across the city. Some were physically moved for hundreds of meters (yards) from a protest sit-in in front of the first security checkpoint near the summit grounds.

None of the activists managed to push into the no-go zone around the summit that the police had established.

The city has boosted its police with reinforcements from around the country and has 20,000 officers on hand to patrol Hamburg's streets, skies and waterways.

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Vladimir Isachenkov contributed to this report.