Brussels (AFP) - Belgium, one of only a few countries to allow euthanasia, on Wednesday moved a step closer to extending mercy-killing to terminally-ill children.

A proposed draft bill to extend the practice some experts say already takes place outside the law was approved by the Senate's justice and social affairs committee after months of discussion held alongside a heated public debate.

The committee's approval enables the draft bill to be put to the vote in the two houses of parliament in the coming months.

The proposed legislation would allow the euthanasia of terminally-ill minors so long as they are judged capable of deciding for themselves and are in pain that is "unbearable and cannot be alleviated".

They would be advised by a medical team and their parents' approval would be required.

A recent poll shows three quarters of Belgians approving the move.

Earlier this month, 16 paediatricians called on lawmakers to approve the legislation.

"Why deprive minors of this last possibility," they said in an open letter carried in the press, arguing that under-18s were able to make an informed and mature decision when facing death.

"Experience shows us that in cases of serious illness and imminent death, minors develop very quickly a great maturity, to the point where they are often better able to reflect and express themselves on life than healthy people."

But a group of Christian, Muslim and Jewish leaders have opposed the legal change. "We express our deep concern at the risk that such a grave subject will be increasingly trivialised," said the group.

"The euthanasia of fragile people, be they children or incapable, is totally inconsistent with their condition as human beings."

A 2002 law made Belgium the second country in the world after The Netherlands to legalise mercy killings for those suffering from incurable illnesses.

Unlike Belgium, however, the Dutch law allows euthanasia for children over 12.

In 2009, Luxembourg also approved euthanasia, for adults only. In Switzerland, doctors can assist a patient seeking to die but euthanasia itself is illegal.

The issue is hugely controversial and raises a host of ethical problems but a majority of Belgian lawmakers is thought to favour the change.

Belgium logged a record 1,432 cases of euthanasia in 2012, up 25 percent.

There are strict conditions for euthanasia including that patients must be capable, conscious and have to present a "voluntary, considered and repeated" request to die.