The United Nations International Children's Emergency Fund (UNICEF) has expressed concern about the humanitarian conditions of Yemeni children, warning about the formation of a "lost generation".

More than half a million children have been forced to leave their homes in the past six months, most of which have fled a major Saudi-led military onslaught on Yemen's port city of Hudaydah during July and August, said the Yemen director of UNICEF, Meritxell Relano, on Thursday.

Facing no access to education and withstanding an increased risk of disease and hunger, Relano highlighted some of the conflict's long-term effects on the children.

“Without education they will not be able to find jobs... a generation that is not educated has a very bleak future,” said the UNICEF director.

“We are losing a generation - many children are losing on their education, and displacement makes it worse.”

The Save the Children charity reports that despite an ongoing ceasefire in Hudaydah, thousands of families are still fleeing the city in fear of a renewed Saudi siege. Many are struggling to afford basic items like food, fuel and medicine.

“Children forced to flee their homes often have to live in unsanitary and cramped conditions in camps or host communities with little access to clean drinking water or nutritious food,” said Save the Children spokesman Bhanu Bhatnagar.

Bhatnagar added that children are specifically vulnerable towards malnutrition, diarrhea, cholera, and diphtheria -- a serious bacterial infection that spreads as easily as a common cold. As much as 89 percent of Yemen's diphtheria deaths are related to children who are under 14.

Saudi Arabia and its allies unleashed the deadly military aggression against Yemen in March 2015 in an attempt to reinstall the country’s former Riyadh-allied regime.

Yemen’s Houthi Ansarullah movement, which runs state affairs in Sana’a in the absence of an effective government, has been defending the nation against the Saudi aggression.

In June last year, the Saudi-led coalition launched an offensive on Hudaydah despite international warnings that it would compound the country’s humanitarian crisis.

Hudaydah is known to be the point of entry for 80 percent of the country’s commercial imports and nearly all UN-supervised humanitarian aid.

The Saudi-led offensive has destroyed Yemen's infrastructure and led to famine in the import-dependent state.