The boy is currently being treated at a nearby children's hospital and is said to be in a stable condition.
In Britain, public concern for Ashya's immediate health has shifted to sympathy for the family's plight as well as anger, particularly on social media, at their pursuit by police.
Police had warned that Ashya's life was in danger if he was not in hospital, but his father and one of his brothers insisted in videos posted to YouTube that he is being cared for properly.
The family's local MEP said the parents should be released immediately to be with their child.
However, the local elected police and crime commissioner, Simon Hayes, defended efforts to bring Ashya home.
"I think if Hampshire Constabulary (police) had ignored the professional medical advice and opinion, then they would have been negligent in their responsibilities to safeguard Ashya in this case and young children in general," he told BBC radio.
Prime Minister David Cameron, who lost his six-year-old disabled son Ivan in 2009, said the priority should be to ensure that Ashya receives the most appropriate medical care.
His spokesman added: "Of course, I am sure that every parent wants to do the best for their child. That is probably the most human of human instincts."
No charges yet
Ashya's father wants his son to undergo proton beam therapy, an alternative to radiotherapy treatment which Britain's state-run National Health Service (NHS) would not provide.
The family was hoping to sell their apartment in Malaga to raise funds for the therapy, which is available in the United States and the Czech Republic, their lawyer said.
The hospital in Southampton, southern England, that was treating Ashya said it had offered the family access to a second opinion on his treatment and offered to help with organising treatment abroad.
But in a video filmed shortly before his arrest, King, 51, said he was threatened with losing access to his son if he continued to criticise the care provided.
Following the family's flight, the local authority obtained temporary wardship of Ashya -- giving them legal powers over his care -- and ordered that he "be presented for medical treatment".
A clinic in the Czech capital Prague, which King had contacted, has now offered to treat Ashya if he is eligible, the BBC reported.
King and his wife, 45, were arrested under a European warrant issued for "an offence of cruelty to a person under the age of 16 years", Britain's Crown Prosecution Service (CPS) said.
But prosecutors have yet to decide if the Kings should face charges.
Ashya's grandmother, Patricia King, said his parents and six siblings had not been able to see him since the arrest, saying the situation was "absolutely disgraceful".
"They (the authorities) are the ones who are cruel because they have taken poor little Ashya, who is dying of a brain tumour, and they won't let the parents, my son and daughter-in-law, they won't let them see him at all," she told the BBC.
- AFP
