Amid the angry tears and prayers for peace and justice for those Australians killed on flight MH17, one simple message rang true: "Let's bring them home."

The words were uttered by Governor-General Sir Peter Cosgrove but his lament was shared by some 2000 mourners at Sydney's St Mary's Cathedral. Millions more were pausing to grieve for the at least 37 Australian citizens and residents shot from the sky over Ukraine, Sir Peter said on Sunday.

"Their lives were taken in an absence of respect and dignity and humanity," he said. "Our overriding wish is that we can give them that love and respect and dignity in their passing. And we say: let's bring them home."

Their bodies remain adrift thousands of kilometres away, some lying neglected and exposed in a foreign field – bodies mangled beyond recognition, passengers still strapped in their seats.

"It is a harrowing image to see fields of crops in eastern Ukraine strewn with human remains and wreckage," said Bishop Peter Comensoli.

In the targeting and destruction of flight MH17, "the shocking effects of our fallen humanity have once again confronted the world", he told those gathered at St Mary's.

"The downing of MH17 was not an innocent accident; it was the outcome of a trail of human evil. Consider how blame and buck-passing is the current strategy of those responsible," he said.

"Evil will try to hide, obfuscate, deny. Yet by the light of day the true picture will be seen."

Among the toll of 298 dead was Sister Philomene Tiernan, a long-time teacher and boarding mistress at Sydney Catholic girls school Kincoppal-Rose Bay. Her current and former students were among mourners gathered in the chill and gloomy morning. Some wept and hugged each other after the special mass of remembrance.

"She was such a welcoming person," said ex-student Anna Fernon, 20. "I remember when I was in my final year, she would always come around to each of the girls' rooms to make sure we were all going OK."

"Sister Phil", as she was known, was flying home from the Netherlands after commemorating the death of her uncle, a pilot shot down over Amsterdam during World War II.

"For her, it was the trip of a lifetime," said Anna's mother, Michelle. "She was in a good space when she died. I hope she was asleep when it happened."

Prayers at the mass spoke of forgiveness and mercy, along with justice for those killed when MH17 was shot down by a surface-to-air missile.

"It's a world that's out of control when people do that sort of thing," said Catholic school teacher Ann Freeman. "It's devastating. It's a gross miscarriage of justice."

Prime Minister Tony Abbott and Opposition Leader Bill Shorten were also among the congregation. A national commemorative service would be held in about a fortnight, "when the families and loved ones of those who are dead have more time to come to terms with their grief", Mr Abbott said.