China Railway Corp has fixed problems found in tunnels along the Shanghai-Kunming high-speed railway to ensure safe and interruption-free operations, the company said in a statement on Thursday.

Some tunnels in the Guizhou section of the Shanghai-Kunming high-speed line developed cracks and leaks as a result of heavy rains over the summer, signaling potential safety hazards.

"The railway department has always prioritized safety for the railway and passengers, and no safety hazard is acceptable. The railway department will never ignore any construction or engineer ing quality problems. They must be fully rectified," the company said. "The department will identify the responsible parties, which will be punished in accordance with the law and their contracts." Thepaper.cn reported on Tuesday that serious problems were discovered in some tunnels along the Shanghai-Kunming high-speed railway, including substandard construction materials that posed safety risks.

Companies involved in the construction, design and inspection of the tunnels have been punished, according to the report, which did not elaborate.

The 2,252-kilometer line opened in late December and is the nation's longest east-west high-speed line. It traverses five provinces - Zhejiang, Jiangxi, Hunan, Guizhou and Yunnan - and cut rail travel time between Shanghai and Kunming from 34 hours to 11 hours.

It is one of China's most important high-speed lines, linking the less-developed southwestern region to the eastern coast. It is also the first high-speed railway in Yunnan, home to many ethnic groups.

China has the world's largest high-speed rail network with 22,000 km of track in use, accounting for 60 percent of the high-speed service worldwide.

The total length of China's high-speed railways will reach 38,000 km by 2025, and 45,000 km by 2030, according to a plan released by the National Development and Reform Commission in July last year.