French energy giant Total announced Thursday it had found "significant" gas off the southern coast of South Africa, a discovery expected to boost the nation's struggling economy and reduce reliance on imports.

Total's CEO Patrick Pouyanne said the potential quantities "could be around one billion barrels of global resources, gas and condensate light oil".

"So it could be quite big, it's probably quite big," he told journalists in Paris.

"Having said that this region is quite difficult to operate, with huge waves, so the weather is not very easy," he said of the block with water depths ranging from 200 to 1,800 metres.

South Africa's Mineral Resources Minister Gwede Mantashe welcomed the news of the discovery in the deep waters as "potentially a major boost" for the economy which grew less than one percent last year "It is exciting for our country. We welcome it as we continue to seek investment to grow our economy," the minister said.

The news came just hours before President Ramaphosa delivers a state-of-the-nation address, his final one before crucial elections due in May this year.

Analysts see the deep water find as a potential "game-changer" for the continent's most industrialised country.

Total said it was planning to drill up to four more wells on the same block.

"In fact, if the gas find indeed proves to be very large, Brulpadda could answer one of South Africa's most intractable dilemmas - how to replace coal in the energy mix," said Ben Payton, an analyst with London-based Maplecroft.

"Using natural gas from Brulpadda as feedstock for gas-to-power plants would reduce or eliminate the need to import LNG or construct additional pipelines from Mozambique," he said.

Andrew Latham of the natural resources consultancy Wood Mackenzie said that while the well is not an oil discovery "if Brulpadda proves to be anywhere near as big as the estimates of up to 1 billion barrels of oil equivalent resources, it will still be a game-changer for South Africa".

South African mining analyst Makwe Masilela said the discovery was "positive" for South Africa, which is desperately seeking foreign direct investment and to cut down on gas imports from neighbouring Mozambique.

"Foreign direct investment is something we are seriously looking for as a country," he told AFP on the sidelines of a mining investment conference in South Africa.

"With this discovery, Total has opened a new world-class gas and oil play and is well positioned to test several follow-on prospects on the same block, " said Kevin McLachlan, Senior Vice President Exploration at Total.

Total holds a 45 per cent stake in the block, alongside Qatari, Canadian and South African firms.

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