Police have said “time is running out” as they continue searching for the five-year-old boy with a brain tumour whose parents took him yesterday from a Southampton hospital.

Ashya King was taken from Southampton General Hospital on Thursday afternoon at 2.25pm, crossing the Channel on a ferry at 4pm with his parents and six siblings.

Assistant Chief Constable Chris Shead said if Ashya “doesn’t receive urgent medical care or the wrong treatment is given his condition will become life threatening”.

“Time is running out for this little boy. We need to find him and we need to find him urgently.”

On Friday evening, Interpol issued a global alert for Aysha's return, and tweeted a Yellow Notice featuring a photo of the child. The notices are circulated to help locate missing persons, especially minors, the organisation explained.

(Facebook/Naveed King)

Ashya was receiving treatment for a brain tumour, undergoing a major operation seven days ago. He is in a wheelchair and unable to speak, eating only through a battery operated tube - due to run out today.

Patrica King, Ashya's paternal grandmother, praised her son and daughter-in-law, describing them as "wonderful".

Ms King admitted this afternoon she last spoke to her son "a while ago", adding: "He wouldn't have told me anything because he wouldn't want me to know anything in case I got involved in it all."

In pictures: Ashya King's case Show all 22 1 /22 In pictures: Ashya King's case In pictures: Ashya King's case Ashya King Brett King, back left, and Naghemeh King, right, accompany their son Ashya King (5) center, as he arrives for pre-cancer treatment examinations at the Motol hospital in Prague, Czech Republic In pictures: Ashya King's case Ashya King Ashya King (5) arrives for pre-cancer treatment examinations at the Motol hospital in Prague, Czech Republic In pictures: Ashya King's case Ashya King Brett King, father of five year old Ashya King, talks to members of the press after holding a press conference at his lawyer's office in Seville, Spain In pictures: Ashya King's case Ashya King Brett and Naghemeh King, parents of Ashya King, attend a press conference in Sevilla, Spain. The British parents are heading to see him at a hospital in southern Spain following release their from custody after United Kingdom authorities dropped accusations of child cruelty against them In pictures: Ashya King's case Ashya King British couple Brett (L) and Naghemeh (2L) King leave Soto del Real Prision in Soto del Real, near Madrid, Spain In pictures: Ashya King's case Ashya King Brett King leaving Soto del Real prison near Madrid, Spain after British authorities dropped the case against him and his wife for taking their son Ashya from Southampton General Hospital without the consent of doctors In pictures: Ashya King's case Ashya King Naghemeh King leaves Soto del Real Prision in Soto del Real, near Madrid, Spain In pictures: Ashya King's case Ashya King Ashya King in hospital with his mother In pictures: Ashya King's case Ashya King Journalist work outside the Materno Infantil Hospital where Ashya King is hospitalized in Malaga, Spain In pictures: Ashya King's case Ashya King Ethan Dallas and Sanjay Ganatra, friends of the family, deliver a petition of over 100,000 names calling for his parents' release from a Spanish jail PA In pictures: Ashya King's case Ashya King Spanish judge Ismael Moreno arrives to the National Courts to take statement to the parents of Britain's five-year-old boy Ashya King, in Madrid, Spain In pictures: Ashya King's case Ashya King Ashya King parents's lawyer, Juan Isidro Fernandez Diaz, arrives at the National court in Madrid AP Photo/Andres Kudacki In pictures: Ashya King's case Ashya King Spanish policemen stand guard as a police van carrying the parents of Ashya King arrives at the courthouse in Madrid JAVIER SORIANO/AFP/Getty Images In pictures: Ashya King's case Ashya King Ashya King’s parents after their court appearance BBC In pictures: Ashya King's case Ashya King Ashya King's father explained why he took his son to Spain in a video uploaded to YouTube In pictures: Ashya King's case Ashya King This photo of Ashya King being examined by doctors in hospital was posted on Facebook by his brother, Naveed Facebook/Naveed King In pictures: Ashya King's case Ashya King Ashya King and his brother Naveed Facebook/Naveed King In pictures: Ashya King's case Ashya King Ashya King on a hospital bed Facebook/Naveed King In pictures: Ashya King's case Ashya King A CCTV still issued by Hampshire Police of Ashya King with his father Brett King at around 4pm yesterday PA/Hampshire Police In pictures: Ashya King's case Ashya King The exterior of Southampton General Hospital where Ashya King, who has a brain tumour was taken by his parents from the hospital without the blessing of doctors In pictures: Ashya King's case Ashya King Hampshire Constabulary said there are 'serious concerns' for the life of Ashya King as he needs constant medical care. Officers said his parents - Brett, 51, and Naghemeh, 45, - boarded a cross-Channel ferry from Portsmouth to Cherbourg at 4pm yesterday with Ashya's six siblings PA/Hampshire Police In pictures: Ashya King's case Ashya King Ashya King, who has a brain tumour and was taken by his parents from hospital without the blessing of doctors

It has been confirmed that the parents are Jehovah's Witnesses, although there is no suggestion this is linked to why they were taken. Police have said it was “irrelevant” while the search for the boy continued.

A spokesperson for the Jehovah's Witnesses said: "There is absolutely no indication, as far as we are aware, that their decision is in any way motivated by any religious convictions. Jehovah's Witnesses are encouraged to seek the best medical treatment for themselves and their children."

His parents, Brett King, 51, and Naghemeh, 45, from St David’s Road, Southsea, Protsmouth, boarded a cross-Channel Brittany ferry from Portsmouth to Cherbourg at 4pm yesterday.

Brett, 51, and Naghemeh, 45 (PA/Hampshire Police)

Although Ashya left the hospital at 2.25pm, police were only notified at 8.35pm that evening – by which point the family were already in France.

A spokesman for University Hospital Southampton said: “Ashya was a long term patient who was permitted to leave the ward under the supervision of his parents as part of his ongoing rehabilitation. When the length of time he had been absent became a cause of concern to staff yesterday afternoon they contacted police after a search of the site and attempts to contact the family were unsuccessful.”

Police confirmed French authorities are also working on the search, emphasising they had every reason to believe Ashya was still in France.

A CCTV still issued by Hampshire Police of Ashya King with his father Brett King at around 4pm yesterday (PA/Hampshire Police)

The family are travelling in a grey-colour Hyundai I800 Style CRDI, registered KP60 HWK.

Assistant chief constable Shead said they hope the King family saw the appeal and realise the gravity of the situation.