Leaders of the world's top economies have arrived in Germany for the start of the G20 in Hamburg, where large groups of protesters are rallying against the summit.

The meeting in the port city in the country's north comes at a time of major shifts in the global geopolitical landscape, with US President Donald Trump's "America First" policies pushing Europe and China closer together.

More than 100,000 demonstrators are also expected to descend on the city to protest against everything from climate change policies to capitalism.

Amid seemingly intractable conflicts, the host, German Chancellor Angela Merkel, faces the daunting task of steering leaders towards a consensus on trade, security, climate and migration - all issues that have become more contentious since Trump entered the White House in January.

Merkel said she hopes to find "compromises and answers" on a range of issues at the two-day meeting.

All eyes on Trump

All eyes will be on the US president, who will make his maiden appearance at the summit.

Al Jazeera's James Bays, reporting from Hamburg, said the highlight of the Friday will be the meeting between Trump and Russian President Vladimir Putin, an encounter that will be intensely scrutinised following allegations by US intelligence agencies that Moscow meddled in the US election.

Trump said in a tweet he was looking forward to the meeting.

Bays said Trump and Putin have "important issues to discuss, particularly Ukraine, but also the issue of Syria where, it is believed, there may be a new initiative coming from Russia and the US to try to get the political track moving and to try to get some stabilisation zones around Syria".

Trump's meeting with Putin will take place at the same time as a closed-door meeting on climate change, which could be "a bit of a sign" about Trump's policies on the climate, Bays said.

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The summit is the first meeting of world leaders since Trump announced that the US would withdraw from the 2015 Paris climate agreement, deeply disappointing Merkel, France's Emmanuel Macron and other US allies who had hoped to maintain momentum in the battle against climate change.

The summit will also bring together Trump and Chinese President Xi Jinping at a time when Washington is ratcheting up pressure on Beijing to rein in North Korea after it test-launched an intercontinental ballistic missile.

Among the other issues expected to be discussed at this year's G20 are the conflicts in Syria and Ukraine, and the state of the global economy.

Mass protests continue

Large widespread protests have already taken place across Hamburg and more are expected throughout Friday and Saturday.

On Friday morning, police clashed with protesters who torched patrol cars and blocked roads.

Late on Thursday, a peaceful marched turned violent when police used water cannon, pepper spray and batons to disperse marchers who they say attacked them with bottles and other objects.

More than 75 officers and dozens of protesters were injured.

Al Jazeera's David Chater said that these protesters want to be heard and make an impact.

"There are so many issues involved politically in the G20 summit," he said.

"They are against the globalist capitalist system, they are against Trump's attempts to pull out of the climate change accords. They're essentially protesting every single issue that's going to be raised in this G20 summit."

Many other groups are calling for peaceful protests and are pushing the G20 leaders for action to fight climate change and address economic disparities in the world. Some are even calling for the dissolution of the G20 itself so that the United Nations becomes the platform for such discussions.

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