HAMBURG:  For the 1,000 hard-left militants who wreaked havoc on the streets of Hamburg , German Chancellor Angela Merkel could not have chosen a better location to hold the G20 summit.

The dense, urban environment allows them to disperse and hide easily, and the city is full symbols of the wealth they detest - from the gleaming 800 million euro ($913 million)Elbphilharmonie concert hall to the shipyards that build luxury yachts.

As the July 7-8 summit started on Friday, Black Bloc anarchists and other anti-capitalist protesters sat in groups on main intersections, blocking streets and bridges leading to the summit venue as well as a road used by trucks at Hamburg Port.

On Thursday night, they hurled beer bottles, blocked roads using trash bins and set cars on fire.

A Black Bloc activist who gave her name as Noura blamed police intransigence for the violence.

"The police represent a government that says it is open and tolerant," said the 27-year-old, who came from the western town of Krefeld and was trying to talk male friends out of hurling beer bottles at riot police.

"We just want them to listen to us and take our ideas seriously," she said. "How do they want these young people not to be angry when they dismiss them all as a bunch of violent thugs?"

The Black Bloc movement, which gained prominence in the 1980s with violent protests against nuclear power and squatter evacuations, wants to end capitalism and replace it with a libertarian system void of state power and money.

Hamburg locals watched the violence unfold from their balconies on Thursday night, as police officers in full riot gear chased groups of mostly teenage Black Bloc activists who splintered when they saw the police approach, hiding in alleys on a hill on the northern bank of the Elbe River.

The militants' youthful agility helps them evade arrest by policemen hampered by heavy anti-riot armour and age. Only 29 activists have been arrested so far and more than 100 policemen have been injured.

Outside an underground station near the summit venue, riot police officers readying for an advancing group of protesters told a German woman driving a large black Audi with two children to speed away, as her luxury vehicle could be a target.

Several Black Bloc youth responded with "Get lost!" when approached by journalists, fearing that reporters wearing helmets were undercover police.

Their actions have led Finance Minister Wolfgang Schaeuble to cancel a discussion with pupils at a school in the city and police have used water cannon to clear roads that G20 officials will use to reach the summit venue.

Many locals are angry that Hamburg is hosting the summit, concerned it will cost millions to clean up the city.

"We feel helpless," said Rebecca Schmuck, 28, standing with friends on a slope overlooking the fish market where police stopped the main protest on Thursday after Black Bloc activists refused orders to remove their masks as required by German law during public demonstrations.

"I am against violence but I do understand the Black Bloc," said Schmuck. "Police should have ignored the few of them wearing masks and maybe no violence would have happened."