What is the hottest stock market in the world?

While the U.S. equity markets have started the year with a whimper, there's one stock market that's red hot: China.

The Shenzhen Composite, which represents 40 private companies such as Internet TV and set-top maker Leshi Internet Information and Technology, has jumped more than 47 percent this year. By comparison, the Dow Jones industrial average has slipped 0.3 percent this year.

While the Shenzhen Composite represents just one of China's stock indexes, others have also shown strong gains, with the Shanghai Composite jumping 18 percent since year start. The surge may be surprising given that the country's economy has been slowing, but investors are putting money into the market in the hope that the government will take stimulus actions to spur growth.

Investors may put putting their money into equities for other reasons, as well. Chinese investors are hampered by low interest rates, while the property market has shown weakness, making the equity market look more appealing.

But there are some signs of trouble, with The Washington Post noting that margin accounts more than doubled in 2014, indicating that Chinese investors are taking out loans to buy stocks. Such accounts carry higher risks, as investors can lose more money than they've actually invested.

The market is also getting a lift from millions of newbie investors, with the rally attracting 2.8 million first-time stock pickers to the Chinese equity market in a two-week period in February, Bloomberg News notes. Two-thirds of those new investors lack a high-school education.

Given those trends, it's no wonder that there are concerns the Chinese market has entered bubble territory. Rising prices may depend on new investors continuing to put money into stocks. As Blackfriars Asset Management Ltd. emerging markets head Tony Hamm told Bloomberg this week, "It'll be good for the market as the bubble expands," he said. "But it will surely end in tears."