Of the 17.1m food insecure people about 7.3m are considered to be in need of emergency food assistance.
The preliminary results of the Emergency Food Security and Nutrition Assessment (Efsna) show that food security and nutrition conditions are deteriorating rapidly due to the ongoing conflict.
More than two-thirds of Yemen's population of 27.4m people now lack access to food and consume an inadequate diet.
The Efsna is a joint survey conducted by the Food and Agriculture Organisation of the United Nations, Unicef and the World Food Programme, in cooperation with the authorities in Yemen. It is the first national, household-level assessment conducted in the country since the escalation of the conflict in mid-March 2015.
Rates of acute malnutrition were found to have passed the "critical" threshold in four governorates, while agricultural production is falling across the country.
"The speed at which the situation is deteriorating and the huge jump in food insecure people is extremely worrying," said Salah Hajj Hassan, FAO Representative in Yemen.
"Bearing in mind that agriculture is the main source of livelihood for the majority of the population, FAO is urgently calling for funds to scale up its agricultural livelihoods support to farmers, herders and fishing communities to improve their access to food in 2017 and prevent the dire food and livelihood security situation from deteriorating further."
The severe food insecurity situation in the country has worsened sharply in recent months, with an estimated 65% of households now food insecure. More than half of all households have had to buy food on credit, and 60% have been forced to make adverse eating decisions, like skipping meals or substituting foods.