More than a half-million children in Yemen face life-threatening malnutrition as the risk of famine grows, U.N. Children's Fund (UNICEF) senior official said Friday. The figure, a three-fold jump since fighting escalated in March, reflects depleted food supplies exacerbated by a failing healthcare system unable to care for hungry children or vaccinate them against disease, said Afshan Khan, the director of UNICEF emergency programs. "We are facing the potential of a huge humanitarian catastrophe," Khan told Reuters. "The levels of malnutrition that are being reported for children are extremely critical." "A nutritional survey will be done at the end of October. How close are we to a famine declaration? We see some zones that are worse than others," she said. In addition to 537,000 children under age five at risk of severe acute malnutrition, 1.3 million are moderately malnourished, according to the latest U.N. figures. Fewer than one in five therapeutic feeding centers in Yemen are functional, Khan said. UNICEF operates 43 mobile teams that screen children for malnutrition, but areas such as the al Qaida-held eastern province of Hadramawt are inaccessible.