The International Committee of the Red Cross on Monday said 184 people had died of cholera since April 27, with another 11,000 suspected cases diagnosed across the country.
This is the second outbreak of the disease in less than a year in Yemen, where less than half of the country's medical facilities are functional two years into a war between Iranian-backed Huthi rebels and the Saudi-supported government.
The Huthi-run health ministry on Sunday warned it was "unable to contain this disaster", in a statement on the rebels' Saba news agency.
It launched an appeal for help from international humanitarian organisations to deal with the crisis.
Hafid bin Salem Mohammed, the rebel health minister, said the "scale of the disease is beyond the capacity" of his department, in a statement on Huthi-run Al-Masira television.
The state of emergency is an "indication of how serious this crisis is", United Nations humanitarian coordinator in Yemen Jamie McGoldrick told reporters on Monday.
"This rapid outbreak of cholera is just another dire manifestation of the humanitarian catastrophe that faces this country," he said.
"These numbers will increase in the weeks and months ahead," McGoldrick warned.
Dominik Stillhart, the ICRC director of operations, told AFP: "Hospitals are already overstretched due to the armed conflict and now the high influx of cholera patients is choking the health system country-wide."
France said on Monday it was "preoccupied by the rapid spread" of cholera, pledging two million euros ($2.2 million) to support programmes "responding to the extremely urgent needs" in Yemen, mainly in the health sector.
"It is more than ever urgent to find a political solution in Yemen, the only way possible to end the suffering of the population," a French foreign ministry statement said.
International relief agencies on Sunday warned of a catastrophic humanitarian situation and urged citizens to exercise hygiene precautions.
