UK firm Tullow Oil has announced the discovery of 600 million barrels of light oil offshore from Ghana.

Reserves in the Mahogany exploration well were far greater than the 250 million barrels than the firm had earlier forecast.

The Tullow chief executive, Aidan Heavey, said it was one of the biggest oil discoveries in Africa in recent times, but warned it could be up to seven years before the oil started to flow.<

Meanwhile, Ghana's President John Kufuor says the discovery of the country's first major oil deposit could turn the West African country into an "African tiger".

"Even without oil, we are doing so well... With oil as a shot in the arm, we're going to fly," he told the BBC.

"My joy is that I'll go down in history as the president under whose watch oil was found to turn the economy of Ghana around for the better," he said.

The discovery of 600m barrels of light oil offshore was announced on Monday.

Reserves in the Mahogany exploration well were far greater than the 250 million barrels than UK firm Tullow Oil had earlier forecast.

Tullow, which saw its shares rise more than 12% on the news, jointly owns the West Cape block where the drilling took place with Anadarko Petroleum.

Mr Kufuor said the discovery would give a major boost to Ghana's economy.