Violent protests have left at least 76 police officers injured as world leaders arrive in Hamburg ahead of this weekend’s G20 summit.

German police deployed water cannons and pepper spray against protesters on the eve of the summit, after masked activists threw bottles and firecrackers at police officers.

Some 12,000 protesters joined the so-called “Welcome to Hell” demonstration, with about 1000 covering their faces – which is illegal during protests in Germany.

Organisers declared the protest over after vain attempts by police to separate the violent protesters from the peaceful ones.

It had been scheduled to finish later on Thursday at Reeperbahn — the epicentre of the city’s red-light district — just 300 metres from the summit venue.

Police said that “several” people had been injured in the “heavy riots”, but could not confirm the exact number, while three officers were taken to hospital.

They added that police spokesman Timo Zill had been attacked by protesters, but had managed to flee unscathed after hiding in an ambulance.

A protester throws an object into a fire ‘Schanzenviertel’ quarter close to ‘Rote Flora’ building. Photo: EPA

Masked protesters smashed windows at stores and vandalised cars in the carnage.

“We are appalled,” Hamburg police wrote on Twitter.

Protest organiser Andreas Blechschmidt said German authorities and the country’s domestic intelligence service had conducted a “massive campaign” in the run-up to Thursday’s event to defame participants and deter people from joining.

Police water cannons in operation during the protest “G20 Welcome to hell” in Hamburg. Photo: AP

The protest remained peaceful until about 5pm local time, with some 1400 people gathering at Hamburg’s Fischmarkt — a fish market near the harbour dating back to 1703 — to hear speakers denounce the leadership of the G20.

The main G20 protest is scheduled for early on Saturday and is expected to bring together 100,000 protesters from a web of civil society, environmentalist and political groups.

Hamburg’s chief of police, Ralf Martin Meyer, said he suspected G20 protesters were behind an overnight arson incident at a local Porsche dealership in the city.

Eight cars were nearly destroyed by the fire in the suburb of Eidelstedt.

German leaders, including Chancellor Angela Merkel, have supported the right to peaceful protest surrounding the summit.

Turnbull speaks out

The protests came as Prime Minister Malcolm Turnbull expressed confidence that leaders of the G20 nations would agree on tougher sanctions against North Korea and extremism.

Police were unable to sort peaceful protesters from violent one. Photo: EPA

Mr Turnbull’s optimism ahead of the Hamburg meeting, which is due to begin on Friday, comes despite deep divisions over what steps to next take to ensure North Korea abides by United Nations sanctions against testing missiles.

North Korea’s “reckless and provocative” action has been condemned by all G20 members, the prime minister told reporters in Hamburg.

“We will see a strong commitment … to strengthen the sanctions that have already been applied to the North Korean regime,” he said.

“We need the 20 largest economies of the world to pull together and support each other in delivering the security that all of our citizens deserve and are entitled to expect from their leaders.”

Asked about the US taking military action, Mr Turnbull declined to speculate but reiterated Australian action would be done under the UN, as well as autonomous sanctions targeting North Korean individuals and businesses.

He also urged China to do more to “bring economic pressure in particular to bear”.

– with AAP