The United Nations on Wednesday declared Yemen a level-3 humanitarian emergency, the highest on its scale, to step up urgently-needed international aid for the war-torn country.
UN aid chief Stephen O'Brien met with heads of agencies to discuss the crisis in Yemen, where a Saudi-led coalition has been carrying out air strikes to push back a rebel offensive.
"All agencies agreed to declare the level three for a period of six months," said UN spokesman Farhan Haq.
More than 21.1 million people -- over 80 percent of Yemen's population -- are in need of aid, with 13 million facing food shortages.
Access to water has become difficult for 9.4 million people, according to the UN.
Under the emergency plan, the United Nations will try to reach 11.7 million people in Yemen who are the most in need.
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"The health system is facing imminent collapse with the closure of at least 160 health facilities due to insecurity, lack of fuel and supplies," he said.
UN Secretary-General Ban Ki-moon has repeatedly called for a humanitarian ceasefire to allow badly-needed aid to be delivered to civilians suffering from the air war and the rebel offensives.
The United Nations has also pushed the coalition to allow more commercial cargo ships to reach ports in Yemen, which is heavily dependent on imports of food, fuel and other vital supplies.
Ten of Yemen's 22 governorates are classified as food emergencies -- one step below famine, according to the UN.
Yemen slid deeper into turmoil when the Saudi-led coalition launched air strikes in late March to stop an advance by the Iran-backed Huthi rebels who drove the president into exile.
Saudi Arabia and its Gulf allies are demanding that the Huthis pull back from territory seized in their offensive and that President Abedrabbo Mansour Hadi be restored to power.
A week of UN-brokered talks in Geneva earlier this month failed to narrow differences.