Violent protests erupted in Hamburg, site of the G-20 summit, as thousands of leftists and anarchists gave German authorities all they could handle.

AFP:

On Thursday night on the eve of the summit of the leaders of the world's top 20 economies including US President Donald Trump, a protest march in this port city by 12,000 people quickly got out of hand.

After a hard core of around 1,000 black-clad militants ignored authorities' demands to remove their masks, riot police moved in with water cannon trucks and tear gas.

That set the stage for hours of running battles between police and protestors in the back streets of Germany's second city that left 111 police officers injured, authorities said.

It was unclear how many protestors were hurt. Organiser Andreas Blechschmidt criticised what he said was a heavy-handed and "massive" police response with batons.

Police, with a sweeping bird's eye view through half a dozen helicopters, coordinated from a high tech centre, were quick to respond with riot police, water cannon and tear gas.

US President Donald Trump's armoured presidential limo dubbed "The Beast" made it through but other leaders including the president of Indonesia and delegations were delayed, reporters said.

Local resident Benjamin Laub, 53, said his neighbourhood has resembled a zone "under a state of emergency" for days.

All of this violence was caused not solely by a few hundred anarchists.  The massive police presence could have handled that number of violent protesters fairly easily, as we've seen during summits in the past.

These protests are radically different.  It appears that anti-Trump hysteria has unhinged many on the left, giving them an excuse to torch cars, battle police, and otherwise disturb the peace of Hamburg. 

No doubt the majority of protesters wanted to make their point peacefully.  But the incendiary mix of anarchists and anti-Trump hysterics turned Hamburg into a war zone.