TAIPEI—China’s tech giants are feeling the pinch of an economic slowdown, adding financial pressure to an industry beset by a bevy of new regulations this year.

Some of China’s largest tech companies have attributed weaker July-September revenue growth to deteriorating macroeconomic conditions. Social-media and videogaming giant Tencent Holdings Ltd.’s quarterly sales grew at their slowest pace since the company went public in 2004. Online delivery firm Meituan said growth of food delivery orders decelerated. Search-engine...

TAIPEI—China’s tech giants are feeling the pinch of an economic slowdown, adding financial pressure to an industry beset by a bevy of new regulations this year.

Some of China’s largest tech companies have attributed weaker July-September revenue growth to deteriorating macroeconomic conditions. Social-media and videogaming giant Tencent Holdings Ltd. ’s quarterly sales grew at their slowest pace since the company went public in 2004. Online delivery firm Meituan said growth of food delivery orders decelerated. Search-engine company Baidu Inc. reported a slowdown in advertising, while e-commerce giant Alibaba Group Holding Ltd. cut its growth forecast for the fiscal year.

Their latest challenges contrast with the robust results posted by some of their American peers, including Alphabet Inc.’s Google and Microsoft Corp. , which were buoyed by a shift to online shopping and remote work amid the pandemic. While Amazon’s quarterly sales growth slowed amid supply-chain disruptions and labor shortages, both it and Google said demand for digital-ads business was strong.

Chinese internet platforms have already been dealing with the impact of new policies that more strictly control areas like data collection, algorithms and minors’ time online. “The question is whether those platforms are set up to service merchants in what you would describe as recession-proof or crackdown-proof industries. And there’s not many of those at this point in time,” said Michael Norris, research and strategy manager at Shanghai-based consulting firm AgencyChina.

China’s economy grew 4.9% in the third quarter from a year earlier, falling short of economists’ forecasts and slowing sharply from the previous quarter’s 7.9% expansion rate. Recently, economic growth has been weighed down by a host of factors including power shortages, supply-chain issues and a crackdown on private sectors including technology, real estate and education.

Tencent’s quarterly sales grew at their slowest pace since the company went public in 2004

Photo: david kirton/Reuters

For some Chinese internet giants, the economic slowdown has translated into weaker demand for digital advertising.

Tencent’s third-quarter revenue in online advertising rose 5% year-over-year, slowing down from a 23% growth in the previous quarter, as a result of tighter regulation in areas like education, insurance and online videogaming. Meanwhile, other industries have been slow to pick up the slack, executives said.

“Other categories will leap into the gap and sort of backfill and take advantage of the lower prices,” said James Mitchell, Tencent’s chief strategy officer. “I think that will happen over time, but in a more challenging macro environment, it happens less quickly.”

E-commerce platform operator Pinduoduo Inc.’s third-quarter online marketing services sales—largely from digital ads—rose 44% from the same period a year ago, slower than the 64% increase in the second quarter and 157% jump in the first quarter.

On Friday, Beijing’s top regulator published draft rules for the internet advertising industry, including prohibiting after-school training ads targeting young students and holding advertisers and internet platforms accountable for ad content.

Baidu Chief Strategy Officer Herman Yu said the weakness in advertising revenue would likely persist beyond the third quarter, particularly if pressures from Covid-19 shutdowns and increased regulation continue. China has recorded a very small number of Covid-19 cases compared with other countries, yet sporadic outbreaks have continued to result in temporary halts on travel and business.

Third-quarter ad revenue at ByteDance Ltd., which operates short-video platform TikTok and the Chinese version Douyin, has been squeezed despite fast-growing e-commerce operations on those apps, according to company employees. ByteDance isn’t listed and doesn’t release quarterly earnings results.

Singles Day in China is the world’s largest annual shopping extravaganza. Its creator, the e-commerce giant Alibaba, is now exporting the event to the rest of the world as part of its push to challenge Amazon and others. Photo: Geoffroy Van der Hasselt/Agence France-Presse/Getty Images The Wall Street Journal Interactive Edition

Beyond China, ByteDance has been beefing up its operations in international markets. Last week, the company launched an app for sellers on TikTok, its latest attempt to mirror its e-commerce success in China with Douyin, according to people familiar with the matter. It has also relocated some marketing employees from China to Singapore to support TikTok’s advertising and e-commerce business, the people said.

ByteDance referred questions to TikTok. TikTok didn’t immediately respond to a request for comment.

Other companies are also looking to diversify growth drivers as China’s economy flags.

Alibaba said its July-September earnings suffered from slowing domestic consumption as well as increased competition, and expects fiscal 2022 revenue to increase by 20% to 23%, compared with its forecast of nearly 30% in May.

The company has said it is looking to cloud computing and international commerce as areas of growth, though they account for just a fraction of Alibaba’s bread-and-butter Chinese e-commerce business. Meanwhile, Baidu said its core revenue was driven by a 73% year-over-year rise in cloud computing.

—Raffaele Huang and Anniek Bao contributed to this article.

Write to Stephanie Yang at stephanie.yang@wsj.com