Malcolm Turnbull has described a Sydney family's ordeal in the Barcelona attack as "tragic" as hopes of finding missing boy Julian Cadman alive are fading.
Julian's father, Andrew, arrived in Barcelona on Saturday (local time) to try and find his seven-year-old son, who was separated from his badly injured mother in Thursday's van attack.
There has been no official confirmation from authorities or family on whether Julian is alive or still missing but on Saturday Spanish police tweeted all victims were accounted for.
"Neither we were searching nor we have found any lost child in the Barcelona attack [sic]. All the victims and injured have been located," the tweet said.
Tweets on Sunday urged against false reporting and misinformation.
On Saturday evening Australian consular officials and police avoided waiting media and took Mr Cadman from the airport straight to Ciutat de la Justicia, Barcelona's main justice and forensic centre.
It is understood Mr Cadman was then taken to hospital where his seriously injured wife and Julian's mother, Jom, is being treated.
Julian became separated from his mother when a van ploughed into crowds in the city's busy Las Ramblas boulevard on Thursday evening.
British authorities and Spanish police had earlier denied reports Julian, who is understood to be a dual British-Australian citizen, had been found at a hospital in Barcelona.
DFAT said it was working in close co-operation with Spanish and UK officials but declined to comment any further.
"Our prayers go out to all the victims, but we to pray that little boy will be found and will be restored alive to his parents," Mr Turnbull told reporters in Sydney on Sunday.
"It is a very tragic circumstance and one of great risk."
Another Sydney woman, Suria Intan, who was on the last few days of a European holiday with friends, is also in a serious condition in hospital after being injured in the attack.
Ms Intan is a Commonwealth Bank worker who is heavily involved with Hillsong church. A spokesperson told AAP that Hillsong in Barcelona is supporting her and her family.
Foreign Minister Julie Bishop said four Australians were injured in the attack including two Victorian men, who have been released from hospital.
They have been named in media reports as friends Robert Bogdanovski and Anthony Colombini.
At least 100 people were injured and 13 killed in the Barcelona attack claimed by Islamic State.
An attack at a nearby resort on Friday morning killed a woman while five attackers were fatally shot by police.