Prime Minister Scott Morrison has condemned the "devastating" bomb blasts in Sri Lanka and says it's still unclear if any Australians are among the 138 dead and 500 injured in the Easter Day attack on the churches and hotels.
The Australian government is now making "urgent" inquiries to reach people in the capital city, Colombo, where several of the terror attacks took place.
Nine foreigners are believed to be among the dead from the blasts at three churches and three hotels: Shangri-La Colombo, Kingsbury Hotel and Cinnamon Grand Colombo.
"The devastating nature of this horrific attack on innocent lives, simply going about their day, going to worship on the holiest of days of the Christian calendar, is just absolutely devastating," Mr Morrison told reporters at Kirribilli House on Sunday.
"There are many Australians regularly travelling in Sri Lanka and our mission in Colombo will be following through on the safety of those Australians."
The staff at the mission have been confirmed safe but the information coming out of Colombo is "confused", the Prime Minister said, and it's still unclear if any Australians have been caught up in the six blasts.
"I'm sure the information will become even more sickeningly real," he said, offering his support and prayers to Sri Lankans in Australia and abroad.
The Department of Foreign Affairs and Trade is now working to firm up the information as it relates to Australian travellers.
"Following several bomb blasts in Sri Lanka, the Australian High Commission in Colombo is making urgent enquiries with local authorities to determine the welfare of any Australians affected," a department spokeswoman said in a statement.
The spokeswoman said anyone concerned about friends and family in Sri Lanka should contact their loved ones directly and, if that failed, contact the department.
The Prime Minister and opposition leader Bill Shorten are both receiving briefings from the department.
Mr Shorten said the news was "devastating".
"We think also of Australia's beloved Sri Lankan community who will carry an immense sense of shock and sadness today," he wrote on Twitter on Sunday.
Speaking at his annual Easter Sunday address at St Peter's Square, Pope Francis condemned the attacks as "such cruel violence."
"I learned with sadness and pain of the news of the grave attacks, that precisely today, Easter, brought mourning and pain to churches and other places where people were gathered in Sri Lanka," he said told tens of thousands of people in the Vatican.
"I wish to express my affectionate closeness to the Christian community, hit while it was gathered in prayer, and to all the victims of such cruel violence".
There were no immediate claims of responsibility for the attacks in a country which was at war for decades with Tamil separatists until 2009 during which bomb blasts in the capital were common.
The motivation behind the attack and identity of the attackers remains unclear, Mr Morrison said.
"Sri Lanka hasn't seen this form of violence since 2009 when hostilities ceased in that country," he said.
"We do know that innocent lives have been stolen once again."
Crowds of hundreds are flooding Colombo hospitals to give blood, Sri Lankan social media accounts showed on Sunday evening.
Other world leaders, including British Prime Minister Theresa May, Russian President Vladimir Putin and Turkish President Recep Tayyip Erdogan, also condemned the attacks.
May said on Twitter that "The acts of violence against churches and hotels in Sri Lanka are truly appalling, and my deepest sympathies go out to all of those affected at this tragic time."
She added, "We must stand together to make sure that no one should ever have to (practice) their faith in fear."
Putin sent a telegram of condolences sent to his Sri Lankan counterpart saying Moscow remained a "reliable partner of Sri Lanka in the fight against international terrorism."
He voiced confidence that "the perpetrators and the masterminds of such a cruel and cynical crime committed amid the Easter festivities will take the punishment they deserve."
In comments posted on Twitter, Erdogan called the attacks "an assault on all of humanity" and offered his condolences to families of the victims and to the people of Sri Lanka.