Twenty-five-year-old Sydneysider Jack O’Brien is the latest confirmed NSW victim of the MH17 disaster.

The family of a “beloved” young Sydneysider heading home from a European holiday is in mourning, after confirmation he was among those killed in the MH17 plane disaster.

Flags atop the Sydney Harbour Bridge flew at half-mast on Saturday as a mark of respect for the dead.

A nun from the city’s east and a retired teaching couple from Wollongong were among at least 28 Australian citizens who perished when the Malaysia Airlines flight was shot down over eastern Ukraine, killing all 298 on board.

Late on Saturday the grim NSW tally climbed to four, with confirmation 25-year-old Jack O’Brien was also aboard the ill-fated flight.

“The life of our beloved son and brother, Jack, has been ended so suddenly,” the O’Brien family said in a statement.

“We are devastated at his loss, as are Jack’s extended family and friends.

“Jack, just 25 years old, was returning from a fantastic seven week holiday in Europe.

“He was loved so much.”

The family has requested privacy.

Fellow victim Sister Philomene Tiernan, who taught at Sydney’s exclusive Kincoppal-Rose Bay School, was making her way home after a sabbatical in France when she boarded the doomed flight in Amsterdam.

About 200 students, parents, nuns and former pupils gathered at the Saint Mary Magdalene church in Rose Bay for a special memorial mass.

“She was on a spiritual high,” the 77-year-old’s friend and school principal Hilary Johnston-Croke told reporters outside the church.

“I can’t tell you how much she’ll be missed.”

It is not the only NSW school community hit by the tragedy.

Former teachers from the NSW Illawarra, Michael and Carol Clancy, are believed to be among the dead.

Mr Clancy had only recently retired after 22 years at Albion Park Public School, principal Glenn Daniels said in a letter to parents.

“When the school has confirmed details, we will consider how to appropriately pay tribute to Mr Clancy and his commitment to the community,” Mr Daniels wrote.

Mrs Clancy’s daughter Jane Malcolm told Fairfax Media the Kanahooka couple, aged 57 and 64, had splashed out on a rare trip, a three-week European holiday.

“When I spoke to mum at the airport, she was just so excited to be going,” Ms Malcolm said.

“They posted a few pictures of their trip and how much fun they were having. I suppose we won’t get the rest of them.”

Australia’s Ukrainian community was quick to deplore what they believe is the Kremlin’s role in the attack, though St Andrews Ukrainian Catholic Church priest Simon Ckuj has called for calm.

“The events of yesterday have affected us deeply. It may have even shaken our faith,” Father Ckuj told those gathered at a vigil in Sydney’s west on Saturday.

“But we must never fall to the temptation of revenge.”

Many want Prime Minister Tony Abbott to take action by banning the Russian president from the Brisbane meeting of the G20 in November.

Scores of protesters gathered in Sydney’s city centre on Saturday afternoon carrying Ukrainian flags and signs describing Mr Putin as a terrorist and a murderer.

Peter Schmigel of the Australian Federation of Ukrainian Organisations said it was only a matter of time before Mr Abbott told Mr Putin he was not welcome.

“Any independent inquiry into the incident with the aeroplane will find that the people who knocked that plane out of the sky and took the lives of 28 Australians have been backed by Vladimir Putin, materially and otherwise,” he said.

“Someone who breaks international law does not belong at the international table, at G20.”