Nearly 20 humanitarian agencies on Wednesday warned of a “nightmare scenario” after the Saudi-led coalition blocked off all entry points to Yemen, a decision that cuts off life-saving aid and compounds the catastrophe in the war-ravaged country.

“Yemen is the world’s biggest humanitarian crisis, with 21 million people in desperate need of assistance,” said Shane Stevenson, country director for Oxfam. “To prevent more lives from being lost and the needless suffering of millions, it is vital that aid is not delayed or impeded another hour.”

The Saudi coalition—which, with assistance from the U.S., has been waging a military campaign against Houthi forces—announced the closure of all Yemen’s air, land, and sea ports on Monday after the kingdom intercepted a missile launched by Houthi rebels.

Yemen is in the grips of the fastest-growing cholera epidemic on the books, is facing the world’s worst food crisis, and has seen its health infrastructure decimated by the ongoing conflict.

The International Rescue Committee, which is among the signatories to the statement, offers key figures to describe why outside aid is so key:

There are over 20 million people in need of humanitarian assistance; seven million of them, are facing famine-like conditions and rely completely on food aid to survive. In six weeks, the food supplies to feed them will be exhausted. Over 2.2 million children are malnourished, of those, 385,000 children suffer from severe malnutrition and require therapeutic treatment to stay alive.

The coalition stated that humanitarian supplies would be let in, but reports from aid agencies indicate that is not the case.