According to new UN figures, more than 14 million people, about half of the population, are going hungry and are in urgent need of food and medical aid.
Some 500,000 children under the age of five are suffering from malnutrition, with two thirds of them so sick they could die if they don't receive immediate assistance, the UN said.
"At least 370,000 children are suffering from severe acute malnutrition," Mohammed al-Asaadi, a spokesman for the UN children's agency in Yemen told Al Jazeera on Wednesday.
"We're talking about a 50 percent increase compared to the number we had earlier this year."
Severe acute malnutrition is a major cause of death for children under the age of five, and is apparent when a child has a very low weight for their height and becomes visibly frail and skeletal.
Yemen has been mired in a humanitarian crisis since March 2015 when Saudi Arabia launched a deadly invasion to restore power to fugitive former President Abd Rabbuh Mansur Hadi. Since then, more than 9,000 people have been killed and 2.8 million driven from their homes.
The cost of food has skyrocketed since the start of the war, Asaadi said, with dramatic inflation in food and fuel prices leaving the poor vulnerable.
"The people are unable to buy food. Good crops could help the situation, but millions are out of work and countless more displaced. Until inflation is addressed the situation will continue to deteriorate."
Humanitarian groups have struggled to deliver aid to large parts of the country due to the fighting and airstrikes, with the medical aid charity Doctors Without Borders, calling the situation "extremely challenging."