Urgent repairs to avert the collapse of the gigantic, power-generating Kariba Dam between Zimbabwe and Zambia will begin this year after the two neighbours signed $294 million in deals with international investors Friday.

The overhaul project of the world's largest man-made dam will fix deformities and cracks in walls that were discovered in a series of assessments. Those threaten to cause the massive structure to collapse -- an eventuality that would carry unimaginable humanitarian and environmental consequences if water in the 181 billion cubic metre capacity reservoir were freed by a massive breach.

Given the high stakes involved, the European Union, World Bank, African Development Bank and the Swedish government agreed to bankroll the critical renovation effort.

"It was considered an emergency and the EU decided to mobilise funds as it was important to start the rehabilitation as soon as possible," Philipe Van Damme, the EU ambassador to Zimbabwe, told AFP.

Managed by the Zambezi River Authority (ZRA), the dam feeds water to two hydro power stations generating 750 megawatts of electricity for Zimbabwe and 600 MW for Zambia.

Without the repairs, the economic and humanitarian consequences would have been "too ghastly to contemplate", said Zambia's Finance Minister Alexander Chikwanda at the signing ceremony on the Kariba Dam wall.

Were the dam allowed to collapse, Chikwanda noted, the lives of millions of people would be at risk in flooding, and power supplies to the entire region would be substantially reduced. Building a new dam, meantime, would cost $5 billion.

The planned repairs will continue for up to 10 years.

Located 400 kilometres downstream from the famous Victoria Falls on the Zambezi River, the dam was built between 1956 and 1959 on designs by French firm Tractebel Engineering.

The curvature concrete arch dam and its enormous reservoir capacity makes the barrage "exceptional in its size," said Bernard Goguel, an internationally renowned expert on dam surveillance.

Stretching out 617 metres and standing 128 metres high, the dam is a "bit like the Eiffel Tower of the great French engineer Andr� Coyne," said Goguel, who had supervised inspections of the dam for over two decades until 2010.

- Risk of floods -

Experts had warned the structure could collapse after massive outflows of water from the spillways had eroded an area near the dam wall.

Swelling of the concrete wall due to slow chemical reaction over the years is also impeding the passage of water through the floodgates.

A collapse of the dam would result in the loss of a key source of electricity for Zambia and energy-starved Zimbabwe. It could also pose a risk to lives of three million people downstream in Zambia, Zimbabwe, Malawi and Mozambique.

In a recent report the World Bank warned that "after 50 years of operation serving the southern African region, Kariba Dam now requires a series of rehabilitation works for its continued safe operation."

"A failure to invest in the timely rehabilitation of the dam will result in the gradual degradation of key dam safety features."

Dam managers ZRA said the repairs will include reshaping the plunge pool to minimise the scouring of the foundation, and fixing the six flood gates.

ZRA chairwoman Charity Mwansa said the "reshaping of the plunge pool will take three years, while the of the rehabilitation of the spillway gates will take six years with minimal disruptions to normal operations."

"We are going to work night and day to make sure this dam has another 100 years," vowed the authority's CEO Munyaradzi Munodawafa.

Of the loans and grants, the largest chunk -- $100 million -- has come from the EU. The World Bank and the African Development Bank are each chipping in with $75 million in loans. Sweden is giving a $25 million grant.

The repairs will cost $300 million in all and the two countries will pay the difference.