A seven-year-old Australian boy who became separated from his seriously injured mother in the Barcelona terrorist attack remains missing.
Sydney woman Jom Cadman is in hospital but family members do not know what has happened to her son Julian.
Another Sydney woman, Suria Intan, on the last few days of a European holiday with friends is also in a serious condition in hospital.
Ms Cadman and her son were in Spain for a wedding this weekend.
Her father-in-law Tony Cadman said Ms Cadman is in a serious but stable condition in hospital, but his grandson is missing.
"Julian is seven-years-old and was out with Jom when they were separated, due to the recent terrorist activity," he said in a Facebook post.
A friend said Ms Cadman's husband Andrew heard about the terror attack when he turned on the radio at work in Sydney on Friday morning, but was unable to reach her on the phone.
Mr Cadman then discovered his wife was in hospital and his son was missing, the friend identified only as Scott told Sydney radio 2GB.
Scott said Mr Cadman was flying to Spain on Friday night, not knowing his son's fate.
"He's flying to Spain at the moment not knowing whether his son is dead or alive," Scott said.
"They were over there for a wedding for this weekend. My mate stayed here and he's just beside himself."
Ms Intan, a Commonwealth Bank worker was named by Fairfax as also being seriously injured in the attack.
She was due to come home this weekend after a three-week holiday with three girlfriends, Fairfax reported.
Foreign Minister Julie Bishop said four Australians were injured in the attack targeting tourists in the Spanish city's Las Ramblas district.
Two Victorian men were hit by the van driven into crowds on a busy promenade, but had been released from hospital.
At least 100 people were injured in the attack claimed by Islamic State, while Ms Bishop said Catalonian authorities put the death toll at 16.
Australian cyber safety expert Susan McLean was about 100m away as the van zigzagged down the busy avenue, mowing down pedestrians and leaving bodies strewn across the ground.
"All of a sudden there was this tidal wave of people running from both Placa de Catalunya and Las Ramblas towards us screaming, crying and with absolute terror etched on their faces," she said.
Ms McLean, who was separated from her husband in the panic as people were pushed into shops, said the scene reminded her of Melbourne's Bourke Street Mall rampage in January that killed six and injured three dozen people.
"My first reaction was the Bourke Street massacre, because that is what it reminded me of - the vision of people fleeing in just such terror," she said.
One of the first Bourke Street responders, fire brigade Commander Graeme O'Sullivan, and his wife saw the carnage as they enjoyed poolside drinks on a rooftop terrace of their Barcelona hotel.
"We could clearly hear thuds as the vehicle was running into people, and then a short time after that, obviously, several very loud sickening screams from the people involved down at street level," he said.
There are no reports any Australians were involved in two connected attacks in the Spanish towns of Cambrils and Alcanar, both south of Barcelona.