Police have received "positive information" that suggests the family of terminally ill Ashya King may now be in Spain.
The family may be travelling to the Marbella area where they have strong links, Hampshire Police added.
The need to find Ashya is now desperate. It is really important that we find him and ensure he receives medical attention at the earliest opportunity.
We still don’t know whether the King family have any spare batteries for the machine which administers food, the knowledge, or any way of recharging the battery.
Without properly administered food Ashya’s situation is very serious.
Ashya's family took him from Southampton General Hospital at around 2pm on Thursday and travelled on a ferry to France some two hours later.
The grandmother of missing boy Ashya King has defended his parents, saying they were "wonderful" and had been left beside themselves by his illness.
Ashya, who was being treated for a brain tumour, was taken out of hospital by his family yesterday.
Speaking from her home in Southsea, his paternal grandmother Patricia King said she has last spoken to her son "quite a while ago", and did not know whether Ashya's illness was terminal.
Of her son, she said:
He's the most caring and wonderful father you could ever have. The kids love him. We are a very close family. He wouldn't have told me anything because he wouldn't want me to know anything in case I got involved in it all.
I knew he was seriously ill, we all knew that.
The Office of Public Information for Jehovah's Witnesses confirmed that the parents of missing boy Ashya King were followers of the religious movement.
We can confirm that the parents of Ashya King are Jehovah's Witnesses. However, we are not aware of the facts of the case nor the reasons for the family's medical choices, which are personal decisions.
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.
Jehovah's Witnesses refuse blood transfusions on religious grounds but are open to other medical procedures.
Police said the family's religious beliefs were "irrelevant" at this point.
The British police police have requested that the French police put into effect their Child Rescue Alert System - a nationwide operation looking at CCTV and trying to pick up the vehicle registration of their car to try to find a location.
So the question is not if this family will be found, but when, given the urgency of the situation.
And when they are found, Ashya is clearly going to have to be taken to a hospital with the same specialist care that he was receiving at Southampton General.
It's a bold new move to try to improve the standard of food in our hospitals. As part of a national campaign to raise the quality of meals they will have to meet set requirements to provide healthy and nutritious meals for patients. Latest statistics show a wide variation here in the South East. Andrea Thomas reports now from the Kent and Canterbury Hospital which was rated highly. She spoke to patients, hospital matron Wendy-Ling Relph and Health Secretary Jeremy Hunt.
Earlier ITV Meridian's Fred Dinenage spoke to Hugh Adams from Brain Tumour Research and I asked him how dangerous it could be to move a child with a brain tumour?
A major police operation is underway tonight to find a desperately ill five-year-old boy taken from Southampton Hospital by his parents against the wishes of doctors.
Ashya King has a brain tumour and is receiving 24-hour specialist care - without medical treatment, doctors say there are serious concerns for his life.
Police believe his parents, Brett and Naghemeh King, from Southsea, have taken their family to France.
Ashya was taken from Southampton General Hospital at approximately 2pm yesterday afternoon.
Police say his mum and dad, along with Aysha and six siblings, boarded a ferry from Portsmouth to Cherbourg at 4pm - arriving in France three hours later - that's 8pm French time.
They're driving a grey Hyundai hatchback with the registration KP60 HWK. Officers are working with French authorities to try to find them.
Well, our Correspondent, Martin Dowse has more.
Police say time is running out for a five year old boy with a brain tumour from Southsea who was taken from hospital by his parents.
Officers say they have serious concerns for the life of Ashya King as he needs constant medical care.
His parents, who are believed to be Jehovah's Witnesses, took him out of Southampton General against doctors wishes yesterday afternoon, and boarded a ferry to Cherbourg along with his six siblings.
ITV Meridian spoke to Assistant Chief Constable Chris Shead from Hampshire Constabulary.
A spokesperson from the NHS Foundation Trust in charge of the hospital where 5-year-old Ashya King was being treated for a brain tumour has issued a statement. Ashya was taken from Southampton General Hospital by his parents on Thursday without agreement from the doctors treating him for his condition.
“Ashya has a serious condition that requires constant medical supervision and treatment. Following his removal from hospital by his parents yesterday, clinical and security staff referred the incident to Hampshire Police.
“We continue to work closely with them to support the search and investigation and have provided a comprehensive detailed medical report on Ashya to ensure any hospital he is taken to can provide the care he requires immediately.
“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.”