Terrorism, free trade and climate will be on the agenda for what is expected to be a politically charged G20 summit in Hamburg.
Prime Minister Malcolm Turnbull is expected to arrive in the German city on Thursday for a bilateral meeting with host leader Angela Merkel, who not only faces national polls in September but is also resisting US President Donald Trump's "America First" attitude to key issues.
The summit will kick off on Friday with a leader-level discussion behind closed doors on terrorism, at which Mr Turnbull will call for cyberspace to be treated just as seriously as the battlefield in countering Islamic State.
Up to 100,000 protesters are set to march through Hamburg seeking a fairer deal out of globalisation and swifter action on climate change.
More than 21,000 police, dogs, helicopters and water cannons have been brought in to deal with the protests, many of whom have embraced the theme "Welcome to Hell".
On the official agenda is free trade, climate and energy, refugees, African development and health.
Much of the media focus will be on the first face-to-face meeting between Mr Trump and Russian President Vladimir Putin, as relations between the two nations sour over alleged Russian interference in the 2016 US election and differing views on Syria and Ukraine.
The G20 comprises Argentina, Australia, Brazil, China, Germany, France, Britain, India, Indonesia, Italy, Japan, Canada, South Korea, Mexico, Russia, Saudi Arabia, South Africa, Turkey, the US and the European Union.
Also attending the summit will be the Netherlands, Norway, Spain, Guinea, Senegal, Singapore and Vietnam.
