The opening ceremony for the 20th International AIDS Conference took place in Melbourne on Sunday, but rather than it be a celebration, the program served as a memorial to the colleagues missing from the week-long event.

Around 12,000 delegates from about 200 countries gathered at the Melbourne Convention Centre for the official opening, which included a minute’s silence to remember those who died when MH17 was shot down.

“It’s a really important time for what we think everyone needs, which is a space to grieve and to respect the six members of our community that died on MH17,” conference co-chair and infectious diseases physician, Professor Sharon Lewin, said ahead of the ceremony.

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The International Aids Society president, Francoise Barre-Sinoussi, dedicated the conference to those who were killed and a letter of condolence and support was read out by the Dutch ambassador for HIV/Aids, Lambert Grijns.

Meanwhile, a dark, tragic cloud hung over the G20 summit in Sydney as senior government ministers from the world’s richest nations got together to talk trade.

Australia’s Trade Minister Andrew Robb at the G20 Summit in Sydney. Photo: AAP

The MH17 disaster and the escalating diplomatic crisis with Russia loomed large all day Saturday, with delegates offering each other their condolences as they tried to plough on with the agenda.

As president of the G20 this year, Australia was keen to move things along and not allow the destruction of the ill-fated plane in eastern Ukraine to distract from the task at hand.

“There was a sombre mood I think in regard to that terrible event, and it did affect I suspect for a while the sort of mood in the room,” Trade Minister Andrew Robb told reporters after chairing the event.

“But we all had a job to do and got on with it.”

All eyes were on Russian minister Alexei Ulyukayev, the Russian minister summoned for an unexpected meeting with Prime Minister Tony Abbott in the afternoon.

Russian minister Alexei Ulyukayev.

Russia has already slammed as “unacceptable” Mr Abbott’s suggestion that pro-Russia separatists were likely responsible for the deadly attack, using weaponry provided by Russia.

The prime minister wasn’t backing away a day later, saying the evidence was clear.

He also hinted that Mr Putin’s attendance at November’s G20 summit would hinge on Russia’s unequivocal support for an investigation, saying Australia would wait and see what next unfolded.

“Australia is a self-respecting country,” he told reporters in Sydney on Saturday.

“Visitors to this country are people who have done the right thing by this country.”

Opposition Leader Bill Shorten declared Labor would fully support barring the controversial leader from the G20, while Queensland premier Campbell Newman said Mr Putin would not be welcome in his home state if he did not co-operate.