The speed limit had been reduced to 300 kilometres per hour after 40 people died in a high-speed train crash near Wenzhou in July 2011.
The acceleration cuts the 1,318-kilometre (819-mile) Beijing-Shanghai journey to 4 hours and 28 minutes, saving passengers nearly an hour.
Starting on Thursday, a total of 14 trains were running between Beijing and Shanghai at the higher speed daily, the official Xinhua news agency reported.
"These trains are so popular that the tickets for today already sold out a week ago," Xinhua cited Huang Xin, an official with the China Railway Corporation, as saying.
The connection between the two metropolises is one of the country's busiest, carrying more than 100 million passengers a year.
But the expansion -- which has cost hundreds of billions of dollars -- has seen a series of scandals and widespread allegations of corruption, with accusations that safety has been compromised for speed.
In 2013, former railway minister Liu Zhijun was given a suspended death sentence for taking 64.6 million yuan ($10.6 million) in bribes. The sentence was later commuted to life imprisonment.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)