Almost 23,500 suspected cases of cholera have been registered in war-ravaged Yemen in the past three weeks, including 242 deaths, the World Health Organization said on Friday.
"The speed of the resurgence of this cholera epidemic is unprecedented", he added.
Yemen could see 250,000 cholera cases within six months, as death toll rises to 242, World Health Organization says.
He said the number of suspected cholera cases could be far larger than those registered as humanitarian workers cannot access some parts of the country. It warned that a quarter of a million people could become sick by the end of this year.
But the epidemic could not be addressed without ensuring that healthworkers were paid, he said, after seven months of no public sector salary payments because of a central bank crisis.
A cholera-infected man reacts as he lies on a hospital bed in Sana'a, Yemen May 6, 2017.
The official noted that the protracted collapse of Yemen's healthcare system and economy is hampering its ability to contain the enteric infection caused by the ingestion of water or food contaminated by the Vibrio cholerae bacterium.
On Sunday, a state of emergency was declared in Yemen's opposition-held capital, Sanaa, after the outbreak killed scores of people over a two-week period.
A cholera epidemic late a year ago petered out but outbreaks are becoming more frequent.
Cholera is an acute diarrhoeal disease that is transmitted through contaminated drinking water.
Zagaria said the United Nations agencies were preparing to "release an emergency response cholera plan in the next 48 hours", aimed at dramatically scaling up the number of treatment centres and rehydration centres.
He also called for providing Yemeni authorities with needed financial resources to make the necessary infrastructure repairs in order to halt the spread of the disease.
More than 8,000 people have been killed since the Saudi-led Arab coalition intervened to support Yemen's government in 2015, according to the WHO.
According to World Health Organization, more than 240 people have died from cholera in just the last three weeks, out of a total of 23,400 infections.