South Africa will deploy more military doctors to its northern border to help stem the tide of Zimbabwe's growing cholera epidemic, a spokesperson for South Africa's government has announced.

South Africa, the region's major power, will also send clean water and other aid to Zimbabwe, said Themba Maseko, in a sign that leaders fear the outbreak will spread beyond Zimbabwe's borders.

Cholera, a preventable intestinal disease, has killed nearly 600 people and infected almost 13,000 since August, according to United Nations estimates.

However, aid agencies believe many more infections and deaths have gone unrecorded, as patients may have fallen ill and died at home.

Cholera is contracted by consuming contaminated food or water, and symptoms include severe diarrhea.

The outbreak is largely blamed on Zimbabwe's crumbling health-care and water-treatment systems, which have languished under the autocratic rule of President Robert Mugabe.

On Thursday, Zimbabwe declared a national health emergency, according to an announcement issued by state media.

In addition to extra doctors and aid, South Africa also plans to send a fact-finding team to Zimbabwe on Monday. The team will issue a report to President Kgalema Motlanthe and his cabinet ministers before more assistance plans are announced, Maseko said.

"We will continue to work with the World Health Organization's representatives and other donor organizations to provide assistance to medical facilities in Zimbabwe in order to manage and reduce the influx of Zimbabweans into South Africa and other neighbouring countries," Maseko said.

Health officials in Mozambique and Botswana, which border Zimbabwe, are assessing the risk of the epidemic spreading into those countries.

The crisis has led the international community to call for Mugabe to step down.

U.S. Secretary of State Condoleeza Rice said Friday it was "well past time" for Mugabe to relinquish power.

The outbreak is an opportunity for the international community to put pressure on Mugable, Rice said, an effort that should be led by neighbouring southern African countries.

In a statement issued Friday, British Foreign Secretary David Miliband said the outbreak was "a further illustration of the misrule of Zimbabwe's rogue government."

On Thursday, Novel peace laureate Desmond Tutu called for African countries to use military force if necessary to oust Mugabe from office should he refuse to resign.

In an interview with the Dutch current affairs program Nova, Tutu, the retired Anglican archbishop of Cape Town, said Mugabe "is destroying a wonderful country...a country that used to be a bread basket...has now become a basket case itself needing help."

Former South African president Thabo Mbeki has been trying to improve Zimbabwe's fortunes through attempts to broker a power-sharing agreement between Mugabe and his main rival, Norman Tsvangirai.

So far, those negotiations have proved fruitless, while Mugabe blames western sanctions for his country's deterioration.

With files from The Associated Press