The World Health Organization says cholera has killed more than 240 people in Yemen in the last few weeks.
The death toll is up from 115 deaths reported last week by the International Committee of the Red Cross (ICRC).
The WHO also says the number of cholera cases has risen to 23,500, as opposed to 8,500 previously reported by the ICRC.
Many of the victims are children, and experts say there could be as many as 300,000 cases within six months.
"The speed of the resurgence of this cholera epidemic is unprecedented," WHO country representative for Yemen Nevio Zagaria said on Friday.
"We need to expect something that could go up to 200,000 to 250,000 cases over the next six months, in addition to the 50,000 cases that have already occurred," he said.
Earlier this week, the Houthi-run health ministry in the rebel-held capital Sanaa declared a state of emergency, saying the situation had worsened and that it was "unable to contain this disaster."
It launched an appeal for help from international humanitarian organisations to deal with the crisis.
Yemen is in a devastating war between Iranian-backed Houthis and the Saudi-supported government. Less than half of the country's health facilities are functioning two years into the conflict.
Cholera is a bacterial infection contracted through ingesting contaminated food or water. This is the second outbreak in less than a year in Yemen, the Arab world's poorest country.
The WHO now classifies Yemen as one of the worst humanitarian emergencies in the world alongside Syria, South Sudan, Nigeria and Iraq.
The UN has warned that 17 million people – some two-thirds of the population – are at imminent risk of famine in Yemen.
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.