A northbound train on the newly opened Beijing-Shanghai high-speed line broke down on Wednesday, the third such incident since Sunday when services were disrupted by power outages.

The Beijing railway bureau said on its official micro blog that the train encountered "a sudden malfunction and could not operate normally".

Passengers had to take a back-up train, which arrived at Beijing South Railway Station at about 5 pm, two and a half hours behind schedule, the bureau said.

The glitch did not delay other trains running on the 1,318-km line.

The train left Shanghai Hongqiao Railway Station at 9:05 am but made an unscheduled stop at Changzhou, Jiangsu province, at 10:26 am, according to passenger and netizen "Anna Zhang".

"The lights and air conditioning were off ... Passengers pursued train attendants seeking an explanation. We were told that the train might be delayed for 30 minutes because of a problem with the signal system," she wrote.

The train started again at 10:51 am, but again stopped at Zhenjiang, Jiangsu province, at 11:34 am.

After waiting for nearly an hour, passengers were told to board the back-up train, which left at 12:30 pm.

On Tuesday, netizens also reported water leaking from the roof of Nanjing South Railway Station, custom built for the high-speed rail.

The latest incident follows passengers suffering disrupted services on Sunday and Tuesday due to power failures.

Problems on the line, launched on June 30, sparked public criticism on Wednesday.

Service disruptions were initially disclosed by micro-bloggers, and online comments and media reports have cast doubts on the line's reliability. Many Internet users said that they would prefer to travel by plane.

But an opinion piece published by Xinhua News Agency on Wednesday asked the public to be "rational", and more tolerant and patient with the new line.

"You can imagine who would laugh quietly on the side," it said, in an apparent reference to foreign high-speed rail competitors.

The comment cited Japanese media reports and said that even in Japan, widely recognized for its safe and punctual rail service, trains have suffered delays.

But Zhang Quanling, an anchor with China Central Television, said on her micro blog that the railway authorities should cast a critical glance at their operations.

"Why do the public and media express doubt and act 'irrationally'? Because when some (government) departments promote a new thing or a new policy, they only talk about the positive, but avoid mentioning shortcomings," she said. "The public may not buy the words totally, but their expectations are high.

"If the railway department pre-warned that high-speed trains could be disrupted by thunderstorms and gales, or that problems are inevitable in the initial stages, I would not have such high expectations ... Rationality should be fostered from the very beginning."