More than 7 million people in Yemen do not know where their next meal will come from and children are dying from malnutrition.
Yemen has suffered 20 months of conflict, with Saudi Arabia backing the government against Houthi rebels.
The British Red Cross said: "The ongoing conflict in Yemen has devastated millions of people's lives.
"Right now, more than half the population don't have enough food. Almost a quarter face starvation. Families are living with no water or electricity."
The charity said vital support could be given to people in desperate need with the help of the British people.
It said 14 million people did not have enough food, and 3.3 million mothers and children were acutely malnourished.
Less than half the country's health facilities were functioning fully and they faced severe shortages of medicines, equipment and staff, it added. [Source: BBC]
In the midst of conflict, DEC member charities are reaching millions of people across the country with lifesaving aid but much more needs to be done.