Investment by Australian resources companies in Africa has increased to 20 billion U.S. dollars and further investment is expected to follow, Australian Foreign Minister Kevin Rudd said on Wednesday.

About 230 Australian resources companies currently hold more than 650 projects in 43 African countries and territories.

According to Australian Special Minister of State Gary Gray, around 20 companies and 100 projects had been added since the beginning of 2011 alone.

More than 40 percent of all overseas mining projects held by Australian-based companies were in Africa and billions of dollars of further investment was in the pipeline, Rudd said.

"Australian resources companies have well and truly discovered Africa," Rudd told the Africa Down Under conference in Western Australia's Perth on Wednesday via videolink.

"Foreign direct investment to Africa increased from 9 billion AU dollars (9.61 billion U.S. dollars) in the year 2000 to 62 billion AU dollars (66.19 billion U.S. dollars) in 2008, almost as large as China relative to GDP (gross domestic product)," he said.

"And despite all of this, Africa's commodities boom is just starting," he added.

Rudd predicted mining exploration activity was set to surge in Africa.

"Australia is at the forefront of this exploration and investment, and there is opportunity to expand this even further," he said.