German police clashed with violent protesters Thursday in Hamburg a day ahead of the Group of 20 summit, using water cannons, pepper spray and batons to disperse marchers after some attacked them with bottles and other objects.

Reuters reported that dozens of police were injured.

The skirmishes came hours before the two-day gathering of the world's top economic powers gets underway Friday morning in Germany's second-biggest city.

Germany G20 Protest

Police officers and a protest stand on the streets of Hamburg, Germany, before the upcoming G20 summit. (Bodo Marks/dpa via AP)

Its host, German Chancellor Angela Merkel, said she hoped the leaders would be able to find "compromises and answers" on a wide range of issues — although the prospects of finding common ground on climate change and trade were uncertain.

The clashes tarnished the start of a meeting Merkel hopes will cement her role as a stateswoman as she seeks re-election in September.

Merkel, who is campaigning for a fourth term, can ill afford the images of chaos and disharmony that dominated news coverage of the summit.

Thursday evening's protest as the G20 leaders arrived in Hamburg was titled "G20: Welcome to Hell," and a standoff between hardcore anti-capitalist protesters and police developed before the march itself really got going.

Black-hooded protesters attack police vehicle

Police said they repeatedly asked some demonstrators to remove their masks, to no avail. They then decided to separate the group from the rest of the march, which they estimated at 12,000 people.

Black-hooded protesters attacked a police vehicle with bottles and bricks, breaking its window.

Germany G20 Protests

Police officers lead detained demonstrators during a protest against the G20 summit in Hamburg. (Markus Schreiber/Associated Press)

Organizers quickly called an end to the march after the violence broke out, police said. Skirmishes continued, with police advancing down the street with two water cannons while being pelted with bottles by a group of black-clad people.

A nearby building was plastered with the slogan "Borderless Solidarity Instead of Nationalism: Attack the G20." A small group on the roof set off fireworks. Police said windows at a furniture store and a bank were damaged.

Nearly 75 police officers were injured during the violence, with three requiring treatment in hospital, police said. The pilots of a police helicopter sustained eye injuries when laser pointers were directed at them, police said.
 
Protesters damaged cars, set other objects ablaze and threw bottles in roving clashes that lasted until midnight.
 
A Reuters eyewitness saw at least one protester with blood on his face being treated.

100,000 protesters expected

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 the United Nations becomes the platform for such discussions.

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

G20-GERMANY/PROTEST

German riot police use water cannons against protesters during the demonstrations. (Pawel Kopczynski/Reuters)

The northern port 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.

Merkel is also hoping to keep things under control inside the city congress centre where the summit is being held. With guests including U.S. President Donald Trump, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan, the search for compromises is expected to be challenging.

'Free, rule-based and fair trade'

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."

G20-GERMANY/PROTEST

Protesters are pushing the G20 leaders for action to fight climate change and address economic disparities in the world. (Kai Pfaffenbach/Reuters)

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 "G19" statement — without the U.S. — on climate change. That is something that Zhu Guangyao, a Chinese deputy finance minister, told reporters Thursday that Beijing also did not support.

"The policies produced by the G20 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."

With files from Reuters