Speaking on the second and final day of the meeting, Gareth Evans, a former Australian foreign minister and co-chair of the newly-founded commission, said the world had been "sleepwalking" on the issue of atomic weapons for a decade.
"The scale of the havoc and the devastation that could be wreaked by one major nuclear weapons incident alone puts 9/11 and almost everything else [in] to the category of the insignificant by comparison," he said, referring to the 2001 terror attacks in the US.
Representatives from more than a dozen countries including the United States and China travelled to Sydney for the meeting, which aims to push for fresh debate on nuclear non-proliferation and disarmament.
Evans said there are between 13,000 and 16,000 nuclear warheads actively deployed around the world and that it was "really a bit of a miracle" that a nuclear catastrophe had not occurred during the Cold War or afterwards.
"We potentially have very alarming consequences staring us in the face"
"Unless we energise ourselves, unless we re-invigorate a high level political debate which is then accompanied by effective action, we potentially have very alarming consequences staring us in the face," he said.
"We are on the brink of... an avalanche or a cascade of proliferation unless we are very, very careful indeed and find ways collectively to hold the line."
Evans, who now heads the Brussels-based International Crisis Group, had earlier said that curbing the spread of nuclear weapons was as important as tackling the global financial crisis.
The 15-member body was initiated in June by Kevin Rudd, the Australian prime minister, following a visit to the Japanese city of Hiroshima, the site of the world's first atomic attack.
Rudd proposed the commission because he felt that the current Nuclear Non-Proliferation Treaty (NPT) was falling apart.
The Australian government had earlier pledged $2.66m to the commission, which aims to "shape a global consensus" on improving the NPT before the 40-year-old agreement which has yet to be signed by India, Pakistan or Israel, comes up for review in 2010.