NAIROBI, Kenya—Chinese President Xi Jinping has signed a slate of investment deals during a weeklong tour of Africa, feeding into concerns in the West and on the continent over ballooning levels of indebtedness to Beijing and its expanding political footprint.

Already Africa’s biggest single-country trading partner, China has become its biggest creditor, too. It holds at least 14% of the continent’s sovereign debt, having lent more than $100 billion to governments and state enterprises since 2000, according to the Washington-based Brookings Institution.

Mr. Xi started his trip on Saturday in Senegal, adding the West African country to the Belt and Road Initiative that will see China invest more than $100 billion in trade infrastructure in Asia, Europe and Africa.

In Rwanda, he signed agreements in areas including manufacturing and health care before heading to South Africa on Wednesday to attend a summit of the five major emerging economies known as the BRICS—Brazil, Russia, India, China and South Africa. He is expected to stop in the island nation of Mauritius off the East African coast this weekend before returning to Beijing.

China’s Africa strategy has changed dramatically in the past few years. The crash in commodity prices and its own economic slowdown shifted Beijing’s appetite from mining and investing in minerals and other natural resources to building and financing huge infrastructure projects and extending loans to cash-strapped governments.