* Three provinces already have drought declarations
* Areas to be declared key for maize, sugar and citrus (Adds details, background)
JOHANNESBURG, Nov 4 (Reuters) - South Africa's drought-hit northern Mpumalanga and Limpopo provinces will be declared disaster areas for agriculture this week or next, an official said on Wednesday, a development that will make them eligible for emergency assistance from the National Treasury.
Ben Kgakatsi, director of risk management in the department of agriculture, also told Reuters that the sugar-growing province of KwaZulu-Natal would soon be declared a disaster area for agriculture. The province has already been declared as such for general water supplies.
"The assessments are being carried out and then they will submit their applications for disaster declarations to their premiers," he said.
The maize-growing Free State and North West provinces have already been designated disaster areas for agriculture as a blistering drought sucks moisture from the soil and dam levels fall, delaying the planting of crops for the crucial southern hemisphere summer season.
Mpumalanga has a diverse agricultural base, with maize grown in its west and big sugar farms in the sub-tropical east of the province. It is also the main source of coal production in South Africa, an industry that heavily relies on water.
Limpopo is the heart of South Africa's game ranching industry but also accounts for a third of the citrus crop in the world's second-biggest exporter of the fruits. Citrus farmers in the province already face water restrictions.
South African cattle, sheep and goat farmers were urged by the government on Tuesday to cut the size of their herds as drought conditions scorch grazing land.
The South African Weather Service said last week that an El Nino weather system, which was already forecast to bring drought conditions for much of the summer, now looks like it will extend into autumn next year. (Reporting by Ed Stoddard; Editing by James Macharia)