Malcolm Turnbull, Donald Trump and other world leaders will be given a "Welcome to Hell" when they attend the G20 summit in Hamburg.
Police in German Chancellor Angela Merkel's birthplace were given a taste of 30 officially registered protest rallies on the weekend when 10,000 people marched against globalisation.
However, 21,000 police have been brought in to deal with a growing protest movement expected to peak at 100,000, with many rallying under the battle cry "Welcome to Hell".
Mr Turnbull will meet with Chancellor Merkel - who says the protests are a show of democracy in action - on Thursday a day ahead of the summit, which will include discussions on terrorism, free trade, climate and energy, refugees, African development and health.
The prime minister said although the G20 summit had an economic slant, countering terrorism would be a priority in the wake of recent attacks.
"The threat of Islamist terrorism ... is absolutely global and there is nowhere that is far away from anywhere else, particularly in the age of the internet," Mr Turnbull told reporters in Sydney on Monday.
"That increased collaboration in the fight against terrorism is going to be very important."
The summit comes at time of heightened political tension, with the US president at odds with many other G20 leaders on issues from the Paris climate accord to trade and steel imports.
Chancellor Merkel, who is seeking a fourth term in September elections, has vowed to challenge Mr Trump's "America First" stance, arguing the world needs to be more sustainable and inclusive.
"We need the climate protection agreement, open markets and improved trade agreements in which consumer protection, social and environmental standards are upheld," she said in her weekly podcast.
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.
Security in the Asia-Pacific is expected to feature prominently on the sidelines of the summit, as leaders seek to deal with North Korea's ambitions and the militarisation of the South China Sea.
After the summit, Mr Turnbull will hold bilateral talks with French President Emmanuel Macron in Paris and his British counterpart Theresa May in London, as well as meet with the Queen at Buckingham Palace.
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