The planning and design of the project was a result of careful, scientific and thorough surveys and reconnaissance, conforming to national and local standards and there was no "arbitrary decision," a local official said.

Structures that could affect the construction and operation of the No.1 Subway Route had been torn down or removed to protect the environment and people's daily life along the line, the official confirmed.

The constructing method deployed was chosen specifically because it worked well in the region's geological conditions, he added.

He also said the government had planned for a reasonable constructing period: three years to finish the tunnel and another two years to complete the tracks, electricity and trains. Construction bidding followed the regular rules and there was no cut in the budget, he added.

The government admitted to the leak, but said there was no evidence of it being chronic. Besides, construction units were told to set up monitoring spots to send out alarms if they detected problems. The fact was that until the day of the accident there had been no alarms from the construction units.

In recent years there have been a number of accidents involving subway-construction sites across the country. On March 28 last year, a section of Beijing No.10 Subway Line collapsed, killing six construction workers. On April 1, 2008, a subway construction accident in Shenzhen killed three and injured two.

The subway collapse in Hangzhou again highlighted a series of safety problems in the country's construction industry, said a recent statement from the State Administration of Work Safety.

Among the issues on the top of the list were deficient safety measures, neglect of dangers once they are discovered, insufficient or poor training for workers, excessively informal hiring practices, and the failure of quality supervision.

Accident investigators found that one of the main causes of the Hangzhou cave-in was that the protection wall failed to provide enough support.

According to a report from Caijing, the protection wall at the west end of the tunnel was terribly warped. One investigator suggested that contortion of this degree must have happened over an extended period of time.

Many workers onsite also said they had found cracks in the wall but did not bother addressing them. "We saw those problems, but we did not know what they meant," said one worker who survived the disaster. "There was no way for us to report them either."

An anonymous expert said China has the technology to build tunnels under any conditions. It's up to contractors to choose safe methods. Failing that, disaster is imminent.

"If they had strengthened the base first, it's likely they could have avoided this tragedy," said the expert. The method he suggested would have dramatically increased the cost, by 20 to 30 percent at least.

Experts said the Hangzhou tunnel collapse should serve as a warning to officials engaged in metro expansion projects across the country.

China's major cities, including Beijing and Guangzhou, were ordered to strengthen safety measures following the subway tunnel collapse in Hangzhou.

Authorities in Beijing, where seven urban railway lines are being built, intensified checks on all construction sites. They installed closed-circuit TV cameras to monitor sites around the clock, Beijing Youth Daily reported.

According to Nanfang Daily, in Guangzhou, where seven subway projects are under construction, a team of 120 officials has begun daily patrols of more than 200 sites.

Each subway project has a six-person team to monitor the sites deemed most risky.

A recent report by the Development Research Center of the State Council showed that proper safety measures have long been lacking in China's large-scale subway projects.

"The accident in Hangzhou is unlikely to make cities with subway plans slow their pace, but it should make them realize that safety has to be the top concern," said Miao Yanying of the Subway and Metro Railway Research Center under the Ministry of Housing and Urban-Rural Development.