A police hunt is under way for a five-year-old boy with a brain tumour taken from a British hospital by his family.

Ashya King was taken by his parents on Thursday from a hospital in Southampton without consent from doctors, and boarded a ferry to the French port of Cherbourg.

The boy's parents, Brett and Naghemeh King, are Jehovah's Witnesses, but the movement said Friday there was no indication their decision was motivated by religious convictions.

There are serious concerns for Ashya's health.

Interpol statement.

"There are serious concerns for Ashya's health, he is immobile and likely to be in a wheelchair or buggy, and cannot communicate verbally," Interpol said.

The missing persons alert went out to all 190 Interpol member countries, the AFP news agency reported.

Police officials said that if they could not locate the child, his life would be in danger. 

The youngster, who has undergone extensive surgery and was last operated on seven days ago, is fed through a tube on a battery-operated system.

In a statement, the hospital in Southampton 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".

Cherbourg prosecutor Eric Bouillard said authorities considered the boy had been "kidnapped given the circumstances of his departure from hospital".

Jehovah's Witnesses are known for refusing blood transfusions on religious grounds, but they are otherwise open to other medical procedures.

The religious movement said on Friday: "Jehovah's Witnesses are encouraged to seek the best medical treatment for themselves and their children," it said in a statement.

Source: Agencies