GAZA CITY/GENEVA/CAIRO (Reuters) -The hunger crisis in Gaza is at a tipping point, with critically low supplies of fortified milk and special nutritious pastes exacerbating food shortages and pushing greater numbers of children into starvation, according to aid agencies, malnutrition experts and the United Nations.

STORY: "It is a famine that hits the most vulnerable first..."Famine has formally been declared in parts of Gaza, almost two years since Israel's invasion.And critically low supplies of fortified milk and special nutritious pastes are exacerbating the food shortages,

The United Nations on Friday officially declared a famine in Gaza, the first time it has done so in the Middle East, with experts warning 500,000 people face "catastrophic" hunger.

An announcement of famine — as has now happened regarding Gaza — is a complicated decision. Here's what must be considered before such a declaration is made.