Declaring a state of disaster allows international donors to raise money quickly to provide food aid to Zimbabwe, which has said it will step up imports of the staple maize by buying up to 700,000 tonnes this year to avert hunger.
The southern African nation is still struggling to overcome a steep 1999-2008 recession that saw its economy contract by nearly 50 percent. The worst drought in a quarter of a century is expected to exacerbate its problems.
Saviour Kasukuwere, the local government minister, said in a statement late on Thursday the former British colony had received below 75 percent of normal rains, with up to three quarters of crops failing in some regions.
He also said dam levels were falling, and were at an average capacity of 51 percent. Zimbabwe's biggest hydro power plant, Kariba, has cut back electricity generation by 62 percent.
"Given the foregoing ... His Excellency, the President has declared a state of disaster to severely affected areas in communal and resettlement lands of Zimbabwe effective from Feb. 2, 2016," Kasukuwere said.
Kasukuwere said the number of people requiring food aid had risen to 2.44 million, which is 26 percent of the population.
The El Nino weather pattern has brought poor rains to already-parched southern Africa, hitting crops, including in South Africa, the region's biggest maize grower.
Zimbabwe has forecast that the economy would expand by 2.7 percent this year but the World Bank said on Wednesday the drought and weak global commodity prices would see growth of 1.5 percent, the same as last year.
