Prime Minister Malcolm Turnbull has urged Australians "say a prayer" for seven-year-old Julian Cadman, who has been missing in Barcelona since terror attacks rocked the Spanish city.
Speaking in Hobart, Turnbull said the "shocking terrorist attack" had caused several Australians to be injured with serious fears for Julian, whose mother remains in hospital.
"In this attack we have seen Australians injured and there is a little Australian boy whose mother was badly injured and is in hospital and he is lost. He is missing in Barcelona. So, I think we should all in our quiet moments say a prayer for that little boy," Turnbull said on Saturday.
"All of us as parents know the anguish his father is going through and his whole family is going through, as they rush to seek to find him in Barcelona."
Cadman, who has dual British and Australian nationality, remains unaccounted for after the attack in Barcelona's Las Ramblas area.
During the attacks he became separated from his mother Jom, who was seriously injured and remains in hospital in a stable condition.
Spain Terror: 7-year-old Sydney boy Julian Cadman missing after deadly van rampage. His father is boarding a flight to Barcelona tonight. pic.twitter.com/Uvc9a7apGC— 7 News Sydney (@7NewsSydney) August 18, 2017
The pair had been visiting Barcelona to attend a family wedding. Julian's father, Andrew Cadman, is said to be on his way to Spain.
As the search for Julian continues family and friends have taken to social media in the hope he will be found alive.
Julian's aunt, Norma Canaveral, described the little boy as gorgeous.
"He's really gorgeous you know," she told the BBC.
"He likes playing together with my grandson as well ... bowling, playing football, writing, reading the books."
Norma Canaveral, aunt of seven-year-old Julian Cadman who is missing in Barcelona after yesterday's attack, has described him as 'gorgeous'. pic.twitter.com/f7aXALYs7a— BBC South East (@bbcsoutheast) August 18, 2017
At least 13 lives were lost and more than 100 people injured in the attack on Barcelona's Las Ramblas on Thursday.