Ertharin Cousin warned aid funds were running out for forgotten but ongoing humanitarian crises like North Korea or Yemen, as money shifts to conflicts such as Syria, where the media attention is stronger.
"There is no room for donor fatigue," Cousin said at the UN food aid agency's headquarters in Rome.
"The biggest challenge is ensuring we don't forget conflicts that are beyond the attention of the media," said the Chicago native and ex-official in US president Bill Clinton's administration.
WFP supplies aid to about 97 million people in 80 countries, including 20 states that are mired in constant crises like Afghanistan, Haiti or Sudan.
Recent data shows the number of hungry in the world has fallen but still stands at 842 million people.
With an annual budget of around USD 5.0 billion, the organisation last year spent USD 1.2 billion buying emergency food supplies.
"Our needs always exceed the funding that we receive. Significantly," she said, adding: "We have almost a billion dollars shortage between what we have and what we believe is needed.
In the time she has been in office, Cousin said that aid to Syria had been scaled up from supplying 150,000 people to more than six million internally displaced people and refugees now.
WFP operations in and around Syria are costing around USD 31 million a week, but Cousin said this could not come at the expense of other crises.
"We are very concerned about places like Central African Republic and Democratic Republic of Congo where we continue to act," Cousin said.
The WFP has asked donors for USD 47 million to continue supplying aid to North Korea but has only received pledges amounting to 43 per cent.
In Yemen, she said, five million people are going hungry and half of the children in the country are chronically malnourished, but still the donor money could finish by the start of next year.
"The concern is that Syria is receiving so much media attention and a large operation, that forgetting Yemen is easy," she said.
