Prime Minister Justin Trudeau's sunny ways will be tested over the next few days amid tensions both inside and outside the gates of the G20 summit in Germany, where tens of thousands of protesters are already wreaking havoc.

After protesters in Hamburg torched a Porsche dealership overnight, things were relatively calm through the day Thursday until a barrage of firecrackers and bottles aimed at riot police was answered with tear gas and water cannons.

Not far away, the mood was less violent as more than 12,000 activists attending the Global Citizen Festival greeted Trudeau with cheers during a rock concert at an arena in the northwest part of the city.

Trudeau, along with his wife Sophie Gregoire Trudeau, introduced the band Coldplay and spoke of Canada's feminist international development policy, which he said puts women and girls at the heart of Canada's aid efforts.

"That's one of the messages I'll be bringing with me to the G20 Leaders' Summit this weekend, and I hope you'll help to share that message too," he said.

He later returned to discuss the need to eradicate global diseases like polio.

Earlier in the day, Trudeau arrived in the northern port city just hours before U.S. President Donald Trump, whose protectionist rhetoric and stance against climate change action have been said to pose a threat to much of the G20's recent progress.

But in the minutes after Trudeau touched down, all the focus was on his three-year-old son, Hadrien.

After descending from the plane while swinging from his parents' arms, Hadrien walked down the red carpet clutching the bouquet of flowers German officials initially presented to his mother.

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Trudeau, Grégoire Trudeau and their son Hadrien, centre, are escorted by Canada's ambassador to Germany, Stephane Dion, left, after arriving in Hamburg Thursday. (Ryan Remiorz/Canadian Press)

Tensions over Putin and Trump

The moment kicked off Trudeau's visit to Germany, a three-day stay where tensions between other world leaders are high and protesters are already clashing with police in the streets.

At the concert, where mere mentions of Trump or Russian President Vladimir Putin sent the crowd into fits of booing, the Canadian prime minister seemed to be given rock star status among the concert goers.

That's one of the other main events from this summit: Trump's first in-person meeting with his controversial Russian counterpart.

The G20 gets fully underway Friday, but leaders were already meeting each other in bilateral tete-a-tetes Thursday evening.

Trump sat down with German Chancellor Angela Merkel, with whom he shares a fractious relationship. Merkel has made no secret of her plan to isolate Trump and his anti-climate change stance during the meetings, and Trump has criticized Germany intensely over everything from its defence spending to its refugee policy.

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Police officers are silhouetted by fires lit by demonstrators during a protest against the G20 summit in Hamburg Thursday. The leaders of the group of 20 meet July 7 and 8. (Markus Schreiber/Associated Press)

During the concert, Trudeau had meetings in a private suite in the arena with Norwegian Prime Minister Erna Solberg, Argentine President Mauricio Macri and the head of the World Bank, Jim Yong Kim.

Macri and Trudeau will host the G20 and G7 meetings in 2018, and that formed much of the substance of their conversation. Kim, who appears to be quite friendly with Trudeau, brought his sons along to meet Trudeau and then gushed about him prior to their meeting.

Canadians are "all so lucky" to have Trudeau, said Kim.

"He has brought an incredible breath of fresh air, directness, commitment to the issues," said Kim, who later noted that Trudeau's style of leadership brings people together.

Whether he can end up doing that at the G20 is yet to be seen.

Inside the meetings, tensions will flare around everything from climate change to free trade deals, but much of the action is expected in one-on-one meetings between various leaders — to say nothing of the much-anticipated Friday head-to-head between Trump and Putin.

What kind of impact the protests end up having on the meeting will depend on whether they succeed in their goal of blocking entry to the secure zone around the convention centre.

Police have wrapped the area in fencing and razor wire, and 20,000 officers are on hand to try and keep the peace. The protesters have labelled their event "G20: Welcome to Hell."

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Thousands of people attend a protest against the G-20 summit in Hamburg Thursday. (Markus Schreiber/Associated Press)