Hampshire Police have said that officers investigating the case "now believe that Ashya’s family has taken steps to be able to feed him".
Hampshire Constabulary Assistant Chief Constable Chris Shead said:
Health experts tell us with the proper medical care Ashya has a good chance of survival, but he must get that professional care.
The feeding system that Ashya needs and the other associated medical care is complex, and I would appeal to Ashya’s family not to think that they are able to administer this care themselves.
The doctors assure me that proper medical training is required for the level of care that Ashya needs.
I would also appeal to the medical profession, particularly in Spain, to contact the Spanish authorities if they feel that Ashya’s family have presented or made enquiries at medical facilities.
Police have asked anyone with any information about Ashya, or his mum Naghmeh and dad Brett, to call +44 (0)1962 841534 or dial the European emergency number on 112.
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.