Zimbabwe's government is working with agencies to provide food aid for 3.8 million people, the WFP said.
Zimbabwe's government has said it expects its staple maize harvest to fall by almost half this year, to 1.56 million tons from last season's multi-year record of 2.72 million tons, due to poor rainfall in the 2021-22 growing season.
The country requires 2.2 million tons of maize annually for human and livestock consumption.
Rising food prices, coupled with higher fuel costs after Russia's invasion of Ukraine, have driven Zimbabwe's inflation from 61% in January to 285% in August, undermining President Emmerson Mnangagwa's efforts to revive the country's economy.
WFP said it had budgeted $40 million for the food aid program to cushion millions over the peak of the hunger season from October, when poor households run out of food stocks, to March, when harvesting starts.
"I do not think this is a famine as yet, but that does not mean that it is good. We are preparing for a response that will take off in October up to March. We are working with government on a joint plan for the food deficit mitigation program and that is for 3.8 million people," WFP country representative Franscesca Erldelmann told Reuters.
She said the number of food insecure people had shot up from 2.9 million to 3.8 million, warning that more households could go hungry as grain stocks dwindle.
The southern African country has been struggling to feed itself since 2000, when former leader Robert Mugabe championed the seizure of white-owned farms to resettle landless Black people.