BEIJING -- Tencent Holdings, China's second-most valuable company, may have surprised investors last week by the scale of its return to quarterly profit growth after its first decline in 13 years last August. But underneath the cheer, there are signs of disquiet.

Chinese are no longer spending the majority of their online time on Tencent apps, a development that could eventually undercut their allure as an ad platform. According to figures from Chinese app data provider QuestMobile, the share of time Chinese are spending with Tencent services has fallen to 47.7% from 54.3% a year ago.

For a brief time recently, it looked like even WeChat, Tencent's flagship app, might be challenged. The messaging app, which has 1.08 billion monthly active users concentrated in China, is the takeoff point for Tencent's payments service, mobile games and many of its other offerings.

"The main way they use WeChat is a platform strategy," said Matthew Brennan, author of the forthcoming book, "The Story of WeChat," and a Shenzhen-based marketing consultant.

"WeChat is a user acquisition channel for other products. WeChat drives downloads of other apps and products across the Tencent ecosystem."

According to QuestMobile data cited by Nomura in a report last week, 85% of Chinese smartphone users are active on WeChat, with that single app taking up nearly a quarter of online time in the country.

That is "far ahead of any other apps in [the] Chinese mobile internet space, thus empowering WeChat ads with unparalleled reach to and attention span from its audience," the Nomura team wrote. They value Tencent's WeChat-based operations, including ads, mobile games and payments, at $317.9 billion. That compares with the company's current overall market capitalization of 2.76 trillion Hong Kong dollars ($352.46 billion).

So far, WeChat still has strong advertising momentum. Thanks to growth in placements in so-called public accounts open to all app users, within WeChat's Facebook-like Moments feed, and in what it labels mini programs, or apps that launch within WeChat for gaming or other purposes, online ad revenues soared 47.2% to 16.25 billion yuan ($2.34 billion) in the July-September period compared with a year earlier.

Some in China, however, are restless for alternatives to WeChat, which was introduced in 2011. Zhen Luemeng, a media professional in Beijing, said that her peers increasingly see the messaging service as a tool for professional communication and they have been looking elsewhere for a platform to connect with friends.

"People are more and more reluctant to share their lives and moods [on WeChat]," she said.

Phone users like Zhen were thus ripe for an alternative when an app called Zidan Duanxin, or "bullet messaging," arrived on the scene in August.

Backed by the endorsement and financial support of Luo Yonghao, a respected tech entrepreneur and the founder of niche smartphone maker Smartisan, Zidan Duanxin quickly soared to the top of Chinese app download rankings. It won over more than 8 million users, particularly for its advanced speech-to-text function, an important feature for Chinese users. Luo announced the closing of a 150 million yuan funding round for the app and later said 1 billion yuan would be invested over the next half-year to expand Zidan Duanxin's user base to 100 million.

As fast as it shot out, Zidan Duanxin lost momentum nearly as quickly, with downloads plunging through September and the program even being briefly removed from app stores in October over a copyright issue. While looser content controls were part of its attraction, some users complained of vulgar and pornographic messages while others worried about weak security protections.

Irish Lee, a 25-year-old teacher in Beijing who calls himself "a big fan of Smartisan," said he gave Zidan Duanxin a try "to see what is so great about it." He used it for a bit, but then gave up.

"It didn't meet people's expectations," he said. Zidan Duanxin's speech-to-text conversion was "awesome," he said, but not vital for him. "Zidan Duanxin didn't change anything. It's not a necessity. There was a lack of new functions."

Other messaging apps, some developed by startups led by former Tencent executives, still lurk in the background. One of them, Pop, attracted investment last month from an arm of German media company Bertelsmann.

Messaging, though, may no longer be the issue. The emerging battleground is apps featuring short videos. ByteDance, which operates leading short-video service Douyin and others, last month completed a $3 billion fundraising involving the SoftBank Vision Fund that valued the company at $75 billion and is said to be in preparation for an initial public offering.

ByteDance's short-video service Douyun has been a hit with young Chinese.

According to QuestMobile's data, nearly all the decline in Chinese usage of Tencent apps over the past year can be accounted for by higher use of apps from ByteDance, including news aggregation service Jinri Toutiao. According to these figures, ByteDance apps' time share has climbed to 10.1% from 3.9%.

The company is known for using artificial intelligence to tailor its app feeds into an addictive stream based on what a user has looked at previously on the services, as well as the users' profile and preferences. Douyin has also drawn attention by forming links with celebrities who then post videos on the app for their millions of followers. As of October, Douyin, where videos are limited to 15 seconds, had about 400 million monthly active users.

"To reach out to more young consumers, more and more brands are collaborating with Douyin to promote and market their products," said analysts from research company Fung Business Intelligence in a recent report, citing the examples of Michael Kors, Adidas and Dior.

Tencent is quite aware of the threat from ByteDance. In May, it blocked WeChat users from directly sharing Douyin videos while promoting its own multiplying short-video alternatives. The two companies then filed law suits against each other for alleged defamation and unfair competition.

Zhen in Beijing said that her peers are flocking to Douyin, which is known as TikTok outside China, as a platform for relatively unguarded interaction with friends. Nevertheless, she admits, "WeChat is still the most important app."