Gang visited facilities of the African Union in Addis Ababa, including the new headquarters of the Africa Centres for Disease Control and Prevention.
China financed the complex's construction, as it previously did for the headquarters of the African Union (AU) itself, also based in the Ethiopian capital.
China has been Africa's largest trading partner for over a decade. It competes for influence with the United States - which hosted leaders from 49 African countries last month - as well as with former colonial powers such as Britain and France.
"Africa should be a big stage for the international co-operation, not an arena for major countries' competition," Gang said at a news conference with AU Commission chair Moussa Faki.
A trusted aide of President Xi Jinping and former ambassador to the United States, Gang was appointed foreign minister last month. His visit marks the 33rd consecutive year that Africa has been the destination of the Chinese foreign minister's first overseas tour of the calendar year.
Visiting Benin and Gabon shows ambitions to expand Beijing's Belt and Roads infrastructure-building drive - long focused mainly on the Indian Ocean region - into western Africa.
Gang met on Tuesday with Ethiopian Prime Minister Abiy Ahmed and other government officials, and announced a partial cancellation of Ethiopia's debt to China during the visit, though neither side provided details. Ethiopia has borrowed $13.7bn from China since 2000 and has been seeking to restructure its debt to foreign lenders since 2021.
Gang will also visit Egypt, Angola, Benin and Gabon over the next week. Paul Nantulya, a research associate at the Africa Center for Strategic Studies, said the choice of countries reflected China's diversity of interests in Africa.
China has strong security ties to Egypt and Angola. Visiting Benin and Gabon shows ambitions to expand Beijing's Belt and Roads infrastructure-building drive - long focused mainly on the Indian Ocean region - into western Africa, he told Voice of America radio.