Yemen is close to famine after a 25-percent increase in levels of severe hunger this year and an offensive on the main port city of Hodeida, a lifeline for millions, humanitarian organizations warned on Monday.

Thousands more people have been displaced by the conflict and many are having to skip meals and beg on the streets, they said, with an estimated 8.4 million people already on the verge of starvation.

"We perceive the country to be sitting on a knife edge in terms of famine — it could tip at any time really," Suze van Meegen, spokeswoman for the Norwegian Refugee Council, told the Thomson Reuters foundation by phone from Sanaa.