German police braced for a third day of violent clashes with anti-capitalist protesters bent on disrupting the G20 summit of global leaders in Hamburg port, after radicals torched cars, smashed shops and injured officers overnight.
While around 100,000 protestors have staged peaceful marches since Thursday, a hard core of the Black Bloc militants from across Europe have looted stores, set fire to street barricades and hurled bottles and paving slabs.
The head of Hamburg police said he was shocked by the "wave of destructive anger", riots and arson committed by demonstrators since Thursday.
"We have clear indications it is highly likely that these violent perpetrators will mix in with today's demonstration 'G20 - not welcome!' said Ralf Martin Meyer. "It is to be expected that again, no peaceful protest will be possible."
The anti-globalisation Attac movement plans a demonstration of up to 100,000 people on the final day of the summit. Police said some 21,000 people had already gathered.
"Today we will bring our criticism of the G20 and our alternatives for fair global policies onto the streets," said Attac's Thomas Eberhardt-Koester.
"We want to respond to the police violence and senseless destruction of last night," he added.
In the last three days, more than 200 police officers have been injured. Some 143 people have been arrested and 122 taken into custody. The number of injured protestors was not available. On Friday night, special armed police had been deployed with sub-machine guns.
World leaders and officials are putting the final touches to a joint statement on issues ranging from trade to climate change on Saturday, the final day of the summit.
Merkel had wanted to show her commitment to free speech by hosting G20 leaders in Hamburg, a port city with a strong radical tradition, but images of burning cars and shops and streets awash with debris have raised questions about that strategy.
Hamburg residents inspected the destruction on Saturday and said they were angry the summit was taking place there.
"Merkel underestimated the protests. The least she can do now is come visit (the district of) Sternschanze and see the damage for herself," said Kai Mertens, a 50-year-old programmer.
"We are a very liberal district. But what they did here has nothing to do with the G20 or opposition to politics. They were hooligans and many were foreigners," added Mertens.
Police from across Germany have been brought to Hamburg to reinforce the local force. A 27-year old German suspected of attempted murder after pointing a laser pointer at a police helicopter was due to face a judge on Saturday, said police.