Chinese regulators zeroed in on Didi Global Inc. on Friday, days after the ride-hailing company went public, by blocking its China business from adding new users as they review the company’s cybersecurity.

The probe aims at preventing risks related to national data security, the Cyberspace Administration of China said in a brief statement.

The move comes as authorities seek to rein in China’s big technology companies, which have become central to everyday life in Chinese society, and assert more control over data that these companies hold.

Didi Global’s American depositary shares closed down more than 5% Friday in New York, after rising 16% a day earlier. They were still up around 11% from the IPO price.

Didi said it would fully cooperate with the review. “We plan to conduct a comprehensive examination of cybersecurity risks, and continuously improve on our cybersecurity systems and technology capacities,” the company said in a statement.

Didi, China’s dominant ride-hailing firm, was among the 34 technology companies summoned by Chinese antitrust authorities in April. Since then, regulators have conducted on-site inspections of Didi, the company has said in its IPO prospectus.

Though the review was a listed risk factor in the company’s IPO paperwork, the timing of the review announcement—two days after Didi’s stock started trading in the U.S.—surprised some investors. One investor said in a typical stock decline he may buy more shares, but the lack of clarity in timing on the review made that tricky.

Didi’s probe is the first one publicized by China’s Cybersecurity Review Office, a unit under the CAC. According to measures which came into effect a year ago, those under review should receive initial results within 45 days, except in complicated cases.

Didi cannot take new users during the investigation period, allowing competitors to gain market share. That could result in an estimated loss of about 6 million new users in China, according to Cherry Leung, an analyst at Bernstein.

The probe showcases the power struggle between Beijing and China’s high-tech companies such as Didi, said Samm Sacks, a Senior Fellow at Yale Law School’s Paul Tsai China Center.

“Clearly somebody is not happy,” Ms. Sacks, an expert on Chinese cybersecurity, said.

The post-IPO timing of the review differs from the case of financial-technology giant Ant Group Co., whose initial public offering was canceled last year after a speech by its controlling shareholder, Jack Ma, infuriated government leaders and regulators.

Still, Adam Segal, a cybersecurity expert at the Council on Foreign Relations in New York, said that similar to regulators’ measures against Ant, the Didi probe sends a message about the state’s ability to control China’s platform companies.

Didi, which said it provided services to almost half a billion users globally in the year ended in March, collects a range of mobility data from users, which helps it with traffic analysis and technologies such as for autonomous driving.

Didi has previously faced criticism in China over its handling of user data. In 2018, the company tightened privacy settings on passengers and drivers after two incidents in which female passengers were killed by Didi’s male drivers.

The company, which operates in more than a dozen countries, says it follows strict procedures in collecting, transmitting, using and storing user data.

In recent months, regulators have clipped the wings of technology companies of all kinds, including fining e-commerce platforms and food-delivery firms for alleged monopolistic behavior. That culminated in Alibaba Group Holding Ltd. —founded by Mr. Ma and an early Didi investor—being handed a $2.8 billion fine in April for “abusing its market dominance.” Alibaba said it accepted the penalty “with sincerity.”

Other technology giants including Tencent Holdings Ltd. , Baidu Inc. and Didi itself were hit with smaller fines.

Food-delivery company Meituan also was targeted by the regulators for allegedly abusing its market position. Amid public scrutiny, the company’s value fell sharply in May, when its founder, Wang Xing, appeared to have obliquely criticized the government when he quoted an ancient poem on social media.

On Wednesday, its first day of trading in the U.S., Didi’s stock rose slightly after raising about $4.4 billion in its IPO. That still made it the biggest IPO haul for a Chinese company since Alibaba listed shares in 2014, according to Dealogic.

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—Corrie Driebusch contributed to this article.

Write to Liyan Qi at liyan.qi@wsj.com and Trefor Moss at Trefor.Moss@wsj.com