Belgium's MPs are expected to vote on whether to extend a euthanasia law to terminally-ill children, BBC News reports.

The bill seeks to allow children to ask for euthanasia if their illness is terminal, they are in great pain and there is no available treatment.

The lower house is likely to back the bill. To become legal, it then needs to be signed by the king, making Belgium the first country in the world to remove any age limit on the practice.

The signature of the legislation by King Philippe is seen by analysts as a formality.

The proposal has already passed a number of legal hurdles, and appears to have wide support across Belgium, the BBC says.

Belgium passed a law decriminalizing euthanasia for terminally ill people over the age of 18 in 2002.

On the eve of the expected vote, lawmakers clashed sharply in parliament.

Campaigners against the change said vulnerable children could be put at risk, as they were not capable of making such a difficult decision.

Meanwhile, supporters argued that it would allow terminally-ill children to be relieved from endless pain.

The bill - which was already backed by the Senate in December - stipulates a number of caveats on euthanasia: It says the patient must be conscious of their decision and understand the meaning of euthanasia; The request must have been approved by the child's parents and medical team; Their illness must be terminal; They must be in great pain, with no available treatment to alleviate their distress.

Last November, 16 paediatricians urged lawmakers in Belgium to approve the legislation in an open letter. "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," said their statement.

In 2012, Belgium recorded 1,432 cases of euthanasia in 2012, up by 25% from 2011.

Most adults opting for euthanasia were over 60 and had incurable cancer.