The line, which runs roughly the equivalent distance of a journey between London and Gibraltar, will halve the travelling time from the country's capital Beijing to Guangzhou, an economic hub in the south.
The first train along the 2,298km track set off from Beijing at 9am with a train heading in the opposite direction an hour later.
Trains on the line will travel at 186mph with the journey taking around eight hours.
The fastest journey time between the two cities had been more than 20 hours before the line opened.
There are stops in other major cities including provincial capitals Shijiazhuang, Wuhan and Changsha, along the route.
The line is the latest development in the country's expensive high speed railways program.
But the project has hit the buffers somewhat in recent months with part of a line collapsing after heavy rain in March.
A bullet train also crashed in the summer of 2011 killing 40 people.
The former railway minister, who spearheaded the bullet train's construction, and the ministry's chief engineer, were detained in an unrelated corruption investigation months before the crash.
More than 150 trains will run on the line each day according to the Xinhua News Agency which cites the Ministry of Railways.
Railway is an essential part of China's transportation system, and the government plans to build a grid of high-speed railways with four east-west lines and four north-south lines by 2020.
The opening of the new line brings the total distance covered by China's high-speed railway system to more than 9,300 km (5,800 miles) - about half its 2015 target of 18,000 km.
The longest line had previously been the Beijing to Shanghai route which is 1,318km or 819 miles in length.
source: dailymail
