The World Food Programme (WFP) has launched a $331m (£270m) appeal as the country battles the effects of drought, a cyclone and an economic crisis effect.
David Beasley, head of the WFP, said many were “in crisis emergency mode… marching towards starvation”.
Once a regional bread basket, Zimbabwe has suffered years of turmoil.
Ongoing harvests have been severely influenced by dry season and the cost of food has risen forcefully. Low water levels have likewise hit the primary hydro-electric plant at Kariba, activating moving force cuts the nation over.
The nation is likewise confronting a financial crisis emergency and has reintroduced the Zimbabwe dollar 10 years after it was relinquished amid rampant inflation.
Launching the appeal on Tuesday, Mr Beasley said about 2.5 million people were on the cusp of starvation.
“We are talking about people who truly are marching towards starvation if we are not here to help them,” he said.
“We are facing a drought unlike any that we have seen in a long time.”
Zimbabwe’s problems were exacerbated when Cyclone Idai cleared through the region not long ago.
The huge storm, which additionally hit pieces of Malawi and Mozambique, influenced 570,000 Zimbabweans and left countless them destitute.
Last week, Finance Minister Mthuli Ncube said the government had been providing grain to 757,000 homes since January, in both rural and urban areas.
And on Tuesday, President Emmerson Mnangagwa, who took over from long-time ruler Robert Mugabe in November 2017, declared the drought a national disaster.
The UN was already appealing for $294m for Zimbabwe but says it now needs more funding as the impact of the drought has spread.