The trains have been undergoing tests for several months
China has begun running a new service of high-speed trains, capable of speeds of over 200 km/h.
The first of the 140 trains left Shanghai for nearby Suzhou at 0538 local time (2138 GMT on Tuesday).
Chinese railways are struggling to cope with increasing transport demands and the trains are seen as a way to boost passenger capacity.
Last year China carried some 25% of the world's passengers and freight, on only 6% of its railways, local media say.
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It felt like we were travelling on an airplane
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The Chinese Xinhua news agency quoted officials as saying the speed increase would raise passenger capacity by more than 18% and freight capacity by more than 12%.
However, the trains will only be able to reach full speed on 6,000km (3,728 miles) of track. Speed restrictions will be imposed on another 36,000km.
The first train took just 39 minutes to travel from Shanghai to Suzhou, cutting the normal journey time in half, Xinhua news agency said.
"It felt like we were travelling on an airplane," 78-year-old passenger Chen Lijuan told the agency.
Driver Liu Dongwei, who began his career on steam locomotives, said the railways had had six speed increases since 1997, when 40-50km/h was the norm.