The world's first high-speed railway operating in extremely low temperatures will begin service on April 21 that can reach speeds of up to 300 kilometers per hour.

The 921-km line linking Harbin, capital of China's northernmost province of Heilongjiang, and the port city of Dalian, Liaoning province, currently operates at 200 km per hour based on its winter schedule.

Since the line opened on Dec 1, it has withstood tests of extremely low temperatures and inclement weather and proved safe and reliable, said Gao Wen, deputy director of Shenyang Railway Bureau, which manages the line.

By the end of March, there had been 9.4 million passenger trips on the line, an average of 78,000 per day, he said, adding that 136,000 passenger trips were made each day during the 40-day Spring Festival travel peak, substantially alleviating the heavy transport burden in regions along the line.

The top speed of the bullet train on the line will be 350 km per hour, but for the initial stage, they will travel with caution at slower speeds, according to railway officials.

During the line's winter schedule, normally from December to April, trains will travel at 200 km per hour, and for the rest of the year, speeds will reach 300 km per hour. Ticket prices will vary based on the speeds.

After the summer schedule is adopted, the travel time from Harbin and Dalian will be three and an half hours instead of the current five hours and 18 minutes, according to Gao.

Meanwhile, the line will continue operating trains that run at 200 to 250 km per hour to cater to passengers who prefer the lower speed or cannot afford the higher price.

Under the summer schedule, a ticket for a first-class seat on the faster train from Harbin to Dalian costs 645.5 yuan ($104) and a second-class seat 403.5 yuan.

A first-class seat on the slower train costs 454.5 yuan and a second-class seat 238.5 yuan.

"During this past winter, the line withstood as many as 52 snowstorms, and all the infrastructure and equipment functioned well," said Liu Qijun, deputy chief engineer of the bureau.

"Through a large number of tests and four months of commercial operation, we have accumulated much experience such as how to avoid being affected by snow and remove ice that covers the tracks."

Liu said the exact dates of schedule changes are based on weather conditions and whether the speed of each schedule will be accelerated depends on "comprehensive assessments".

Railway technicians are busy conducting the final tests to prepare for the higher speeds starting on April 21.

"In the acceleration tests, we started at 220 km per hour and will gradually speed up from that to 240, then 260, 280, 300 and eventually 310," Gao said.

Tests on wireless Internet access and audio and data recorders are also under way, using equipment and software developed by China, said Ji Zhenhong, a technical official of the bureau.

A host of techniques used in the construction, operation and maintenance were acquired from the Qinghai-Tibet Railway, which also faced complicated weather and geological conditions, said Wang Bin, a publicity official from the China Railway Corp.