Cherbourg police have joined their English counterparts in the search for five-year-old Ashya King, who was taken from hospital by his parents yesterday.
Brett and Naghemeh King took Ashya on a ferry from Portsmouth to Cherbourg, along with his six siblings, and the family are still believed to be in France.
The child underwent emergency surgery for a brain tumour last month and Hampshire police say his life is at risk.
Ashya King's parents told the Daily Mail they fled the UK after being told NHS treatments would leave him with life-long disabilities.
The head of the police force which applied for a European Arrest warrant against the parents of Ashya King has now urged their release.
A British mother whose son's life was saved by proton therapy has told ITV that she defied NHS doctors' advice to pursue the treatment.