Police say Ashya King's health will deteriorate quickly after family took five-year-old from hospital and boarded ferry to France

A major search and social media campaign is under way to find a five-year-old boy with a brain tumour after he was taken from hospital by his parents without the consent of doctors.

CCTV footage showed Ashya King being taken in a wheelchair by his father, Brett King, from Southampton General hospital at around 2pm on Thursday. His family – including his mother, Naghemeh King, and six siblings – then boarded a ferry from Portsmouth to Cherbourg in northern France.

Screengrab of footage of Ashya being taken from hospital. Photograph: Hampshire police/PA

Hampshire police said there were serious concerns for the boy's life as he needed constant medical attention and "time is running out".

Assistant chief constable Chris Shead said: "It is vital that we find Ashya today. His health will deteriorate rapidly.

"Ashya is in a wheelchair and is fed through a tube. The feeding system is battery operated and that battery will run out today.

"He must continue to be fed through the tube by someone with the relevant medical training.

"If he doesn't receive urgent medical care or the wrong treatment is given, his condition will become life threatening."

Appealing directly to the parents and family, he said: "Our message to you is please take Ashya to the nearest hospital immediately. We understand that this must be an awful time for you, but the most important thing is to get the proper medical care for Ashya. Please work with us to provide Ashya with that care."

He urged Facebook and Twitter users to help track down the family, who are believed to be Jehovah's Witnesses, as the force tweeted images of the parents and posted a picture of the type of car in which they are travelling. Jehovah's Witnesses refuse blood transfusions on religious grounds but are generally open to other medical procedures.

Police said the family, who live in Southsea, arrived in France at 8pm local time on Thursday.

Ashya is likely to be in a wheelchair or buggy; he cannot communicate verbally and is immobile.

The family are travelling in a grey Hyundai I800 Style CRDI, registration KP60 HWK, and are still believed to be in France.

"From what we know it is vital that Ashya's conditions mandates that he is fed in that particular way," said Shead.

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

"It is our dearest hope that his parents will hear this appeal, they will recognise the gravity of the situation Ashya is in medically and they will take him to a hospital. But we will continue to look until we find him."

Police were alerted by the hospital at 8.35pm and have been speaking to authorities in France "where we have every reason to believe the family remain". Police said they were looking at why it took six hours for the alarm to be raised. Ashya was at the hospital receiving ongoing treatment for the brain tumour. He has also undergone extensive surgery, with the most recent operation carried out seven days ago.

Police are "keeping an open mind" on what the motive is and refused to comment on speculation the family were Jehovah's Witnesses. "Any religious beliefs are irrelevant at this time. We are talking about a child's life," said Shead.

Police asked for the appeal to be broadcast throughout France and bordering countries, and urged people to share through social networking, particularly those with friends or relatives in France.

Brett and Naghemeh King, the parents of Ashya. Photograph: Hampshire police/PA

In a video posted on YouTube last month, Naveed King said his little brother had been diagnosed with a brain tumour and was undergoing emergency surgery. Speaking into the camera in a direct message to Ashya, he said: "I haven't slept. I've been awake all night worrying. We love you so much. We're all here for you. Everyone is praying for you. We just want to see your smile again.

"No kid at the age of five deserves to have a brain tumour. Let's just hope the doctors know what they're doing and they know exactly where to operate and what to take out, and they take everything out and you can be better.

"And when we look back in 10 years' time, when you're 15, we can actually see that things have changed for the better. Just because they're bad at one point doesn't mean they'll always be bad. I love you so much. I can't wait to see you."

Naveed also posted footage of a visit to his brother in hospital, having to cut away as the young boy broke down in tears.

On 18 August he posted an update on Facebook signed "King family", saying Ashya had been "progressing slowly but continuously with only minor problems along the way".

The post included several pictures, one showing Ashya with his mother and another of a large stitched wound at the back of the boy's head and neck. Naveed wrote: "He is now able to swallow (only liquid things like water and on odd occasions soft yoghurt) but not chew or move his leaps [sic].

"He can also close his eyelids but still struggles in moving his eyes to look at people or things. He is still unable to talk to explain how he feels or what may be hurting him on occasions. As a family we thank everyone who has taken their time in prayer for Ashya to get better and also … the amazing gifts he has received from those prayers.

"He is still far from being a normal child and still not out of the danger zone of where minor issues could cause severe problems for his brain, so please continue to pray for him to have the strength and to be able to recuperate quickly."

Naveed, whose Instagram profile says he is 20, describes himself as a Jehovah's Witness on the social networking site. Friends making comments on his Facebook page also make reference to the religious movement.

University Hospital Southampton NHS foundation trust said Ashya was allowed to leave the ward under his parents' supervision and hospital staff raised the alarm when the length of his absence "became a cause of concern".

The trust said in a statement: "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."

Brittany Ferries confirmed the family had travelled on board its cross-channel ferry and the company was assisting Hampshire police with its inquiries.

A spokesman said the family had declared they were travelling with a child with "special medical needs" at the time of booking.

The Office of Public Information for Jehovah's Witnesses confirmed that Ashya's parents were followers of the religious movement.

A spokesman said: "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."

The family have travelled to Spain by road in the past, and there is the possibility they are travelling through France to Spain.

• Anyone with information which may help locate Ashya should contact Hampshire Constabulary as soon as possible on 101 quoting Operation Aquilion.

From outside the UK, please call on 0044 1962 841534.

In France, please call the emergency 112 number.