Colourful protests, a $270 million cash splash and high-level meetings with regional leaders marked the start of an ASEAN-Australia Special Summit.
Prime ministers, presidents and other dignitaries bounced between bilateral meetings, panel discussions and press conferences on key concerns including regional security, economic ties and clean energy.
There was a touch of pomp and ceremony, including when Prime Minister Anthony Albanese met Malaysian Prime Minister Anwar Ibrahim at Government House, his first high-level meeting of the Melbourne conference.
The nations formalised a suit of agreements on technology, clean energy, sport and education, as Mr Albanese said his government was keen to support Malaysia's investment, development and growth opportunities.
"We share the same aspirations for the region we call home, we believe in an Indo Pacific region that is open, stable and prosperous," Mr Albanese told reporters.
"Where sovereignty is respected and differences are settled through dialogue and agreed rules and norms."
Foreign Affairs Minister Penny Wong used the opening of the meeting to reveal Australia will pump more than $270 million into development, security and climate programs in Southeast Asia.
Senator Wong said conflict in the region would be as devastating to economies and communities as fighting in Gaza and Ukraine, warning the region's character was under threat.
There was a risk of "miscalculation" leading to conflict, she said in comments that did not name but were clearly aimed at China.
"What happens in the South China Sea, in the Taiwan Strait, in the Mekong subregion, across the Indo Pacific affects us all," she told delegates.
Outside the summit, demonstrators staged noisy rallies as dozens of police watched on.
Protesters marched against the military government in Myanmar as they called for ASEAN nations to intervene in the country and for greater humanitarian aid.
Later, cries of "shame" rang out as activists who oppose newly elected President of the Philippines Ferdinand Marcos Jr. carried a black cardboard coffin emblazoned with the words "RIP Democracy".
Security has been bolstered across the city and Victoria Police given special powers under the Terrorism Act as a precaution to protect dozens of leaders and dignitaries.
It's the second time the event has been held in Australia, offering politicians and business leaders a chance to address issue in formal and informal settings.
ASEAN, an abbreviation for the Association of Southeast Asian Nations, is made up of Indonesia, Malaysia, the Philippines, Vietnam, Brunei, Cambodia, Myanmar, Laos, Singapore and Thailand.
Australia is not a formal member but has been a dialogue partner for the past 50 years.
Timor-Leste will also observe the summit.
Mr Albanese said ASEAN was Australia's second largest two-way trading partner when viewed as a bloc and noted more than one million Australians had Southeast Asian heritage.
He is due to meet privately with leaders of the 10 nations in addition to events held in public.
