A family are appealing for help to find their seven-year-old boy who is still missing following the Barcelona terror attack in Las Ramblas.

Julian Alessandro Cadman, who is believed to be of British dual-nationality, became separated from his mother after a van drove into pedestrians in the popular tourist spot, killing at least 13 and injuring dozens more, including Julian's mother.

The boy's grandfather, Tony Cadman, from Sydney, Australia, posted a picture of the seven-year-old as part of a plea for help in finding him.

The post, which has been shared more than 3,500 times in just four hours, said: "My Grandson, Julian Alessandro Cadman is missing. Please like and share. We have found Jom (my daughter in law) and she is serious but stable condition in hospital.

"Julian is seven years old and was out with Jom when they were separated, due to the recent terrorist activity. Please share if you have family or friends in Barcelona."

Prime Minister Theresa May said the government is "urgently looking into reports" a British child is missing.

She added: "The Foreign Office is offering consular assistance to those who were involved in the attack and their families and are working urgently to see if there are others who need their help. But we must work together if we are to confront this evil of terrorism.

"Also, to confront and deal with the perverted extremist ideology which drives it; ridding the internet of poisonous material and ensuring that our police and security services have the powers that they need. Terrorism is the great threat that we all face. But, together, we will defeat it."

Australia's foreign affairs minister, Julie Bishop, confirmed that eight Australians were affected by the attack in Las Ramblas, including four who were injured and one still unaccounted for.

Bishop added: "Of the four injured, that includes one woman, who is from New South Wales in a stable condition but was seriously injured; a second woman, also from New South Wales, is in a serious condition in hospital, she was travelling on a British passport; two young men from Victoria have been injured, they have received treatment at hospital, but both have been discharged."

Spanish police are still searching for the driver of the van used in the attack. Three other suspects, including Driss Oukabir, have been arrested in connection with the attack.

Five terrorists wearing fake explosive belts were shot and killed by police in a second van attack in Cambrils, a coastal town 62 miles southwest of Barcelona. Six people and a police officer were injured in the second attack.

This story has been updated to note the boy is believed to be of dual British nationality.

Julian Alessandro Cadman
Julian Alessandro Cadman is still missing following the Barcelona attackFacebook/Tony Cadman