There were no injuries reported in the incident, but coming so soon after the 310km/h train service's launch it has rekindled concerns about safety first prompted by reports of massive corruption under disgraced former railways minister Liu Zhijun.

Internet users criticised the train's safety record on online forums and on Weibo, the mainland's answer to Twitter, with some questioning whether a thunderstorm could be responsible for the power cut.

There was also confusion over just how long the train was left without power, with an apparent contradiction between the official statement and eye-witness accounts.

An initial report released by Xinhua late on Sunday night said the train was hit by the power cut at 6.10pm, and continued its journey at 7.37pm following a 'rush repair'. However, the Xinmin Evening News quoted passengers on the train as saying it had broken down at around 5.30pm, and did not restart until 8.10pm.

While the train was stopped the carriages were without lighting or air conditioning, one passenger told the newspaper, adding that it grew constantly 'more and more stuffy'.

Another passenger said the train had stopped a second time, about 20 minutes after it restarted.

Railway engineers had earlier said the rail link had a back-up power system which would kick in if the primary power source failed.

Ren Gang, deputy director of engineering at CNR Tangshan Railway, which builds the trains, told the Xinmin Evening News last month that as soon as the train became disconnected from the electricity grid, its own power system would take over to provide emergency lighting, air conditioning and communications for up to two hours.

Questions were being asked yesterday as to why that did not happen on Sunday night.

No one at the Shanghai Railways Bureau, which runs the service, could be reached for comment yesterday.

A Europe-based expert in high-speed rail technology, who asked not to be named, said he did not see any immediate reason to doubt the official explanation of the malfunction.

'I do not know the real cause [of the breakdown] in this case, but technically it is possible,' he said. 'If the thunderstorm hit the electrical system, the system may well be damaged or it may activate the protection mechanism.'

However, while he said he was unaware of similar breakdowns in high-speed systems in other countries, it was impossible to say whether the incident was a cause for concern over the safety of the rail line without knowing the full details and the 'real reason' for the power outage.

221b yuan

This is the cost, in yuan, of the new Beijing-Shanghai railway link

- The journey time between the cities has been halved, to five hours