Pro-Russian rebels are being blamed for shooting down the Malaysian Airlines Boeing 777-200, which was carrying almost 300 people from Amsterdam to Kuala Lumpur.
More than 100 of those killed on flight MH17 were delegates on their way to an international conference on AIDS in Melbourne, Australia.
It was confirmed on Friday afternoon that one Irish woman, reportedly a mother of two from Dublin who had been living in Perth, was among the casualties.
Dublin's Foreign Affairs Minister Charlie Flanagan said: "Sadly, we have learned that one Irish-born citizen was on board the flight to Kuala Lumpur.
"On behalf of the Government and people of Ireland, I would like to convey deepest sympathies to her family, both in Ireland and in Australia, who have suffered this sudden and devastating loss."
World-renowned Dutch scientist Joep Lange, who has been at the forefront of the fight against Aids for 30 years, died with his partner Jacqueline van Tongeren.
Glenn Thomas, a 49-year-old British media relations co-ordinator for the World Health Organisation (WHO) and former BBC journalist, was also among the passengers as were other WHO staff, medical researchers, health workers and activists.
According to the airline, there were 189 Dutch passengers, 44 Malaysians, including 15 crew, 27 Australians, 12 Indonesians, four Germans, four Belgians, three Filipinos, one Canadian and one person from New Zealand on board. Three people are as yet unidentified
Three infants are among the dead as well as a large number of children.
The plane was flying on a usual route that had earlier been declared safe by the International Civil Aviation Organisation, Malaysia Airlines said.
The International Air Transportation Association said the airspace it had been crossing was not subject to any restrictions.
All European flights operated by the airline will be taking alternative routes with immediate effect.
Foreign Secretary Philip Hammond has called for an international investigation to establish what happened to Flight MH17 when it crashed into territory held by pro-Russian separatists.
Speaking at the Foreign Office following emergency talks with ministers and officials, Mr Hammond said: "We're determined to get to the bottom of understanding what has happened here.
"As yet, we do not have any definitive information about how this incident occurred and I don't want to speculate at this stage. We believe that there must be a UN-led international investigation of the facts."
He said Britain was prepared to make Air Accident Investigation Branch assets and specialists available to assist an investigation.
The UK Government's Cobra emergency committee met on Friday morning.
David Cameron said that if Malaysia Airlines Flight MH17 was shot down over Ukraine those responsible "must be brought to account."
The Prime Minister described the catastrophe as "an absolutely appalling, shocking, horrific incident".
Mr Cameron said his thoughts were with the families of the victims.
"If, as seems possible, this was brought down then those responsible must be brought to account and we must lose no time in doing that," he said.
"It is an absolutely shocking incident and cannot be allowed to stand."
The United Nations Security Council held an emergency meeting on Ukraine in the afternoon.
Kiev has branded the event an "act of terrorism" and demanded a UN investigation.
Russian president Vladimir Putin has insisted it would not have happened if the Ukrainian government had agreed to a ceasefire.