LUSAKA, Zambia — U.S. Secretary of State Hillary Rodham Clinton on Friday urged African nations to tear down continental trade barriers and promote business-friendly policies as she called for an increase in commerce between America and Africa, which is rapidly turning to China as its main trading partner.

At the start of a three-nation tour of Africa focused mainly on trade, development and the rights and health of women, Clinton challenged African leaders to adopt reforms that will further integrate the continent's economies by curbing protectionism, reining in corruption and reducing armed conflict.

The first U.S. secretary of state to visit the southern African nation of Zambia in 35 years, Clinton urged officials and entrepreneurs from 37 countries to take advantage of the African Growth and Opportunity Act, an 11-year old U.S. initiative that aims to boost trade with Africa. She noted that since her husband, former President Bill Clinton, signed the act in 2000, non-oil U.S.-African trade has quadrupled to $4 billion. And with the greater prosperity has come greater stability, she said.

"Today Africa is in such strong position to build on this progress," she told the annual conference of AGOA partners. "Yes, there are still many challenges in many areas, but the region is undeniably more stable, more democratic, and more prosperous than a decade ago."

She lamented that African countries are not taking full advantage of the initiative, which allows qualified nations to export thousands of products to the United States duty-free. Only a handful of the 6,500 products covered by the act are actually being sent to America and the most common export is still oil.

Boosting exports will make Africa less reliant on aid at a time when governments in developed countries, including the United States, are being forced to rethink traditional development assistance, she said. Clinton added that increasing intra-African exports will be essential, as will removing thorny trade restrictions, combatting corruption, improving transportation infrastructure and quelling conflict.

"A business is only as successful as the environment in which it operates," she said. "A strong economy requires a supportive business climate that empowers every entrepreneur to do her very best work."

Clinton is the first secretary of state to visit Zambia since Henry Kissinger came in 1976 to lay out the Ford administration's policy for southern Africa as revolts against white minority rule in South Africa and what was then Rhodesia were intensifying.

Clinton arrived in Zambia from the United Arab Emirates, where she attended an international conference on Libya. After Zambia, she heads to Tanzania and Ethiopia before returning to Washington next week.