China has unveiled what it says is the fastest rail link in the world, but the train came to a screeching halt this week, leaving thousands of passengers stranded -- thanks to a law-breaking smoker.

The cigarette smoke triggered a fire alarm Tuesday on the train connecting the southern economic hub of Guangzhou to the central city of Wuhan -- a journey now made at an average speed of 350 kilometres (217 miles) an hour.

The train, which was still in the station when the incident occurred, was able to leave Guangzhou two-and-a-half hours later after a series of safety checks, the official Xinhua news agency reported late Wednesday.

The departures of three trains were delayed as well, the China Daily reported.

"Smoking is strictly forbidden on the Wuhan-Guangzhou high-speed train, even in the toilet," the agency quoted a spokesman with the Guangzhou Railway Group Corporation as saying.

"It could trigger the alarm and even cause equipment failures."

The smoker fled the scene before the alarm sounded, Xinhua said.

The high-speed express launched on Saturday slashes the travel time between Guangzhou and Wuhan, a distance of 1,069 kilometres, from more than 10 hours to just three.

China aims to eventually extend the link from Guangzhou to the capital Beijing.