Police said violence that erupted during marches on Thursday continued into Friday, with protesters slashing the tires of a car belonging to the Canadian delegation to the G20 summit and smashing windows of the consulate of Mongolia.
At least 29 protesters were detained and 111 police officers had been injured as of Friday morning, including three officers who required treatment in hospital.
A police spokesman said only small numbers of far left or anarchist protesters were involved in violence, with the majority of an estimated 100,000 demonstrators in the city remaining peaceful. Some 12,000 took part in the main march.
But while 15,000 police were on hand from each of Germany's 16 states, authorities said they asked for reinforcements late on Thursday after realising the situation on the streets of Hamburg was proving more difficult than expected.
"We have asked nationwide if police forces are available and those requests are being reviewed," a police spokesman said.
On Friday, smaller groups of protesters attacked both manned and empty police cars, one of which was hit by a petrol bomb, police said.
One of the many police helicopters patrolling the skies was nearly struck by a rocket flare, police said in a statement. On Thursday the pilots of another helicopter sustained eye injuries after a laser was directed against them.
Police said they continued to dispel street blockades throughout the port city.
People walk during the protest demonstration at the G20 summit in Hamburg, Germany
Anti-capitalist protesters set fire to cars, barricades, rubbish bins and wooden pallets on Friday as leaders from the world's top economies convened for a summit in the northern German city of Hamburg.
