HONG KONG — American trash has made Zhang Yin China’s richest person.

Zhang started collecting wastepaper in 1990 in Los Angeles and shipping it to China to make the cardboard needed by growing export industries. Her company, Nine Dragons Paper Holdings Ltd., is now China’s biggest packaging maker. Nine Dragon’s stock has risen fourfold since its March initial public offering, pushing Zhang’s fortune to $4.7 billion.

“Other people saw scrap paper as garbage, but I saw it as a forest of trees,” Mrs. Zhang, 49, told reporters last November in Hong Kong. “I had to learn from scratch. The business was just my husband and me, and I didn’t speak a word of English.”

Investors such as Merrill Lynch & Co. and Baring Asset Management are betting on Mrs. Zhang, the daughter of a revolutionary-era army officer, as the Chinese companies that make everything from computers to bicycles demand more and more cardboard boxes. China’s exports have increased fivefold to $762 billion during the past decade.

“The company is the leader in the industry,” a manager of Baring Hong Kong China Fund, Nine Dragons’s fourth-biggest shareholder, Lilian Co, said. “There’s an expanding market and a shortage of supply. We still like her story.”

Mrs. Zhang is the world’s richest self-made woman, ahead of chat show host Oprah Winfrey and the chief executive officer of eBay Inc., Meg Whitman, according to Shanghai-based Hurun Report, which ranks wealthy people in China. Hurun in October said Mrs. Zhang was China’s richest person, topping Huang Guangyu, founder of Gome Electrical Appliance Holdings Ltd.

Zhang’s career tracks China’s economic opening which, since the early 1980s, has been spurred by the production of consumer goods for export.

China is short of lumber and pulp after chopping down many of its forests during Mao Zedong’s Great Leap Forward, a 1958-62 industrialization drive.

“Chinese manufacturers were desperate for scrap paper,” Mrs. Zhang said in November. “All I did was help fulfill a need.”