HONG KONG — Li Ka-shing, a high school dropout who got his start selling plastic flowers, will retire from the empire that made him Hong Kong’s richest man, he said on Friday, bringing a symbolic end to an era when the road to China’s riches went through the onetime British colony.

Mr. Li, 89, who some called Superman for his business acumen, grew his plastic manufacturing business into a sprawling conglomerate. He did so just as Hong Kong was undergoing a transformation from a British trading post into a beating heart of capitalism and the entry point into China, which was then closed off from the world.

But as China grew, Hong Kong tycoons like Mr. Li faded in importance and a new generation of mainland Chinese businesses sprang up. Today, the region’s richest people are Chinese internet titans and property moguls, while Hong Kong over the years has felt the growing influence of mainland money.

“It has now been nearly 78 years since, as a 12-year-old, I escaped from a war to try to find work in Hong Kong so that I could provide for my family,” Mr. Li said in a filing Friday that announced his retirement, referring to his escape from war-torn China in 1940. He said that he planned to focus on his charity, the Li Ka Shing Foundation.