Sydney schoolboy missing after splitting from family in Barcelona attack

A Sydney schoolboy is missing after a Barcelona terror attack which killed at least 13 people and injured more than 100 more.

Seven News reports seven-year-old Julian Cadman was visiting the Spain city with his family to attend a wedding, when the vehicle hit the crowd.

Police are still searching for the driver of the vehicle, who fled on foot after crashing into a newspaper stall.

The boy's mother, Jumarie Carman, is in hospital in an induced coma. Her husband is currently flying over from Australia to search for their son.

Julian's grandfather took to Facebook to plea for help.

"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 7 years old and was out with Jom when they were separated."

The post has been shared nearly 2000 times within four hours.

Hours after the first attack, media reported a vehicle ran over six people in Cambrils, leaving one person seriously injured and another in critical condition. Five attackers were then shot dead by police.