Bullet trains between Beijing and Shanghai will be even faster in just over a month, but it could mean fewer services.
When the new Fuxing trains go into service along the route in September they will be operating at the speed they were designed to travel at 350km per hour.
Running the trains 50km/h faster would increase operating costs by one-third, according to an industry estimate.
But China Railway Corporation has decided to go back to the maximum speed on the Beijing to Shanghai route.
Some 300 government officials took one of the new Fuxing trains for a test ride on Thursday morning, travelling from Beijing South Railway Station to the Jiangsu city of Xuzhou, about 700km away. It took about four hours to complete the return journey.
At the new speed, the journey between Beijing and Shanghai will take 4.5hours - nearly an hour faster than it takes now.
But the faster service is not necessarily good news for passengers, according to Zhao Jian, a professor at Beijing Jiaotong University and a leading researcher on the country’s high-speed railway network.
Most bullet trains would continue to run at the slower speed of 300km/h and operating services at different speeds on the same line would be a "nightmare", Zhao said.
He added that it could increase the risk of collision, so to avoid accidents the railway operator would have to reduce the number of trains on the line.
"There are more than 100 trains passing on the line every day. With the higher speed, that could drop to about 80," Zhao said. "That will not only dent revenues, it will affect passengers too - the intervals between trains will be longer and there will be fewer seats available."
The high-speed service between Beijing and Shanghai is one of the busiest on mainland China. Some 600 million passengers, or nearly half the country’s population, have travelled on the line since it opened in 2011, according to China Railway.