Africa needs $93-billion annually over the next decade to transform its weak infrastructure ? more than twice previously thought, a new World Bank study said Wednesday.

Conducted recently in 24 countries in the poverty-stricken continent, the study showed that poor infrastructure in Sub Saharan Africa slashed national economic growth by two percentage points every year and business productivity by as much as 40 percent.

The report, titled "Africa?s infrastructure: A time for transformation," found that the continent had the world's weakest infrastructure but ironically Africans in some nations paid twice as much for basic services as people elsewhere.

Existing spending on African infrastructure is much higher than the previously known figure of about $45-billion a year, the study said, estimating an annual bill of $93-billion over the next decade.

Almost half of this amount is needed to address the continent?s current power supply crisis that is hindering growth, it said.

The new estimate amounts to roughly 15 percent of the continent's gross domestic product (GDP) and comparable to what China invested in infrastructure over the last decade.

The bank noted with surprise that most of the current spending was domestically financed by African tax payers and consumers.

The study also found that there was considerable waste to address, saying a number of efficiency improvements could potentially expand the available resources by a further $17-billion.

However, even if major efficiencies were gained, it said there was still a funding gap of $31-billion every year ? much of it for power and water infrastructure in fragile states.

Relative to the size of their economies, the funding gap was found to be daunting for the region's low-income countries, particularly now as the world recovers from a recession stemming from a financial crisis.

"Modern infrastructure is the backbone of an economy and the lack of it inhibits economic growth," said Obiageli Ezekwesili, World Bank Vice President for the Africa Region.

"This report shows that investing more funds without tackling inefficiencies would be like pouring water into a leaking bucket.

"Africa can plug those leaks through reforms and policy improvements which will serve as a signal to investors that Africa is ready for business," Ezekwesili said.

The report recommended addressing the $17-billion annual efficiency gap and closing the remaining $31-billion annual funding gap for African infrastructure.

Closing the efficiency gap requires improving management of utilities, ensuring adequate maintenance, promoting regional integration, recovering costs while recasting subsidies to enable broader access, and improving allocation and spending of public resources, it said.

The study proposed the funding gap be addressed through a wide range of sources, including local capital markets, private sector finance as well as traditional donor assistance.