Users say the technology, supplied by Chinese voice technology firm iFlytek Co, allows them to chat faster without having to type or listen to voice recordings - a time-consuming act for the receiver that is considered impolite in WeChat etiquette in China.

WeChat offers a similar voice input function, but it is hidden in the app's interface and not commonly used. It also does not allow voice messages and transcripts to be sent simultaneously, as Bullet does.

Wang Guanran, a Shanghai-based senior analyst with Citic Securities, described Bullet's key advantage as being "lighter" than WeChat.

For example, WeChat's extra functions include payment and gaming, while Bullet only offers messaging and a newsfeed, and its interface allows users to respond to messages in fewer steps.

"In a time of information overload, it makes communication more simple," he said.