Malawi and Mozambique sounded alarm bells on Wednesday over worsening food shortages caused by severe drought as concerns grow over a hunger crisis spreading across much of southern Africa.

Zimbabwe, Lesotho and Zambia are also suffering food supply problems, while South Africa has said the recent drought was its worst in more than 100 years.

"I declare Malawi (in) a state of national disaster following prolonged dry spells during the 2015/16 agriculture season," President Peter Mutharika said in a statement.

"The projected drop in maize harvest is estimated at 12 percent from last year's output.

"More people will be food insecure and will require humanitarian relief assistance for the whole of the 2016/17 consumption year."

Neighbouring Mozambique issued a "red alert" because of drought conditions in the country's central and south regions affecting 1.5 million people.

The government released $9.5 million of emergency aid after 90 percent of crops were destroyed in some areas and thousands of cattle died from lack of water.

The World Food Programme said it was currently assisting nearly three million people in Malawi, with about 23 of 28 districts badly affected.

"The current drought situation in Malawi came on the back of a bad crop last year, due to flooding which affected parts of the country," WFP's southern Africa spokesman David Orr told AFP.

"The situation is quite dire and we believe the worst is still to come. It will take a long time before the situations improves. Any improvement in the next months would be negligible."

- Limited response -

In February, the WFP warned that Malawi was facing its worst food insecurity for a decade. The country has recently suffered flash floods in the north as well as drought.

The United Nations and aid groups in Mozambique have released a total of $15 million since the beginning of the crisis, Michel Le Pechoux of the Humanitarian Country Team (HCT) which coordinates relief efforts, told AFP.

"But the response is still very limited compared to the actual needs, which amount to about $200 million," he said, adding that central Mozambique was the worst-hit area.

Renewed conflict between government troops and the armed wing of main opposition party Renamo since January has also made delivery of aid difficult due to attacks on roads.

"Some drought-stricken districts are located in areas of military tensions and are almost inaccessible," Le Pechoux said.

In Zimbabwe, 2.8 million people -- more than a quarter of the rural population -- do not have enough to eat.

The WFP, which is providing assistance for about 730,000 Zimbabweans, has reported that casual agricultural labourers have no work and many children are missing school because of hunger.

Southern Africa endured a poor harvest last year combined with a strong El Nino weather phenomenon, which resulted in reduced rains across the region.

South Africa, which in the past has exported food to its regional neighbours, is to import maize after last year was the driest year in the country since records began in 1904.