People have filled the streets draped in the beloved colours as PNG marks 50 years since Australia's colonial rule ended, highlighting its culture, dance and music.
Celebrations officially began with a packed flag-raising ceremony at Independence Hill in Port Moresby on Tuesday morning with Australian Prime Minister Anthony Albanese in attendance.
Proud Papua New Guineans gathered in front of a statue of the nation's first prime minister and founding father Michael Somare, where Prime Minister James Marape spoke.
"Out of many, we became one, united under a single flag that was hoisted for the first time," he said.
Dignitaries from around the world are in Port Moresby for the celebrations, including Prince Edward, representing the British royal family, and leaders from across the Pacific.
Mr Albanese said democracy in PNG had "not only survived but thrived" 50 years after the Australian flag was lowered.
"It wasn't torn down, this was a peaceful transition," he said.
At the original independence ceremony held in Port Moresby on September 16, 1975, then prime minister Gough Whitlam said: "Australia could never be truly free until Papua New Guinea was truly free".
Half a century later, Mr Albanese echoed his predecessor's PNG support, saying the nation of more than 1000 tribes and 800 languages had overcome great difficulties.
"That is a great credit to the foresight of people like Mr Somare and other independence advocates," he told Nine's Today show.
"And also, a credit to the legacy of Australia (and) Gough Whitlam's vision in supporting independence for PNG. It's been a very important and significant day."
Mr Marape addressed the country's ills, saying "we still have many pockets of poverty, many pockets of isolation, many pockets of communities that aren't connected with each other".
"The country will stand on firm ground and fix these problems," he said.
Mr Albanese walked part of the Kokoda Track with Mr Marape in 2024 and said he was in awe of the sacrifice Australian soldiers had made to protect their nation and its democracy.
They could not have done that without the support of PNG, creating a close bond between the two countries, he said.
The two nations are due to sign a landmark defence pact on Wednesday that will bring them even closer together, elevating the relationship to the same level as key Australian allies the US and New Zealand.
As a gift to mark their golden jubilee, Australia will help PNG build a new ministerial wing at its parliament.
Mr Albanese announced the support after a well-attended state dinner on Monday night, with former prime minister Scott Morrison among the guests.
"Our support for the expansion of parliament house is an investment in Papua New Guinea's democracy and sovereignty that will benefit future generations," he said.
On Tuesday afternoon Mr Albanese was set to attend a flag-lowering ceremony at Port Moresby's Sir Hubert Murray Stadium to mark the conclusion of formal celebrations.
In September 1975 the Australian flag was lowered there to mark the end of 70 years of Australia's colonial rule, with the PNG flag raised in its place.Â
Festivities conclude on Tuesday evening with a "PNG50 Spectacular" at the capital's Sir John Guise Stadium, a celebration of PNG culture and the nation's journey to independence through music and dance.
On Wednesday, the two leaders will sign the "Pukpuk treaty", named after the pidgin word for crocodile, which will ensure greater integration of the nations' defence forces and set out mutual obligations in the case of either country being attacked.
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