Unofficial market activity has flourished, too: people making and selling shoes, clothing, sweets and bread from their homes; traditional agricultural markets that appear in rural towns every 10 days; smugglers who peddle black-market goods like Hollywood movies, South Korean television dramas and smartphones that can be used near the Chinese border.

At least 40 percent of the population in North Korea is now engaged in some form of private enterprise, a level comparable to that of Hungary and Poland shortly after the fall of the Soviet bloc, the director of South Korea’s intelligence service, Lee Byung-ho, told lawmakers in a closed-door briefing in February.

This market activity is driven in part by frustration with the state’s inefficient and rigid planned economy. North Koreans once worked only in state farms and factories, receiving salaries and ration coupons to buy food and other necessities in state stores. But that system crumbled in the 1990s, and now many state workers earn barely a dollar a month. Economists estimate the cost of living in North Korea to be $60 per month.

“If you are an ordinary North Korean today, and if you don’t make money through markets, you are likely to die of hunger,” said Kim Nam-chol, 46, a defector from Hoeryong, a town near the Chinese border. “It’s that simple.”

‘Competition Is Everywhere’

Before fleeing in 2014, Mr. Kim survived as a smuggler in North Korea. He bought goods such as dried seafood, ginseng, antiques and even methamphetamine, and he carried them across the border to sell in China. There, he used his earnings to buy grain, saccharin, socks and plastic bags and took it back to sell in North Korean markets.

He said he had paid off border guards and security officers to slip back and forth, often by offering them cigarette packs stuffed with rolled-up $100 or 10,000-yen bills.

“I came to believe I could get away with anything in North Korea with bribes,” he said, “except the crime of criticizing the ruling Kim family.”