New competition

The rapid rise of Bullet serves as a wake-up call for WeChat, analysts say, which has seen no serious challenger in China's mobile messaging world since it was launched in 2011.

"The Chinese consumer is considerably more fickle than the global average," Brennan said. "There are always new consumers willing to try new products and platforms."

The other mainstream option for messaging is QQ, with mobile and desktop versions, which is also run by Tencent and is popular among younger people. Liu Hai, 29, an auto engineer in Shanghai, said he downloaded Bullet in part out of curiosity, but also because he was frustrated with the number of work messages cluttering his WeChat account. "There are too many work group messages on WeChat. It feels like I am working all the time. I cannot even block it out on weekends," he said.

Liu said he was impressed with Bullet's speed and voice-recognition technology, which was able to decipher his southern Chinese accent. But he said he lost interest after three days because "nobody is actually on it."

"Also, when chatting at work, speaking to your phone looks kind of stupid," he added.

Smartisan's Luo said on his Weibo account, which has 15 million followers, that Bullet is simply providing a niche alternative to WeChat for users seeking faster communication.

"This is not a WeChat killer. Bullet is still tiny and has a lot to prove," said Brennan, who said it is "very, very difficult" to build a social network and make people stay.

Fans of Luo and Smartisan, meanwhile, are cheering the app's success as a comeback for the struggling smartphone maker.

Xu Kuo, 31, an entrepreneur who describes himself as a hardcore Smartisan fan, said via Bullet: "I am uninstalling WeChat to support Lao Luo."

Xinhua - Reuters