Experts yesterday asked builders to enhance risk awareness to prevent accidents during subway constructions.

Referring to the collapse of a portion of an under-construction subway tunnel in Hangzhou, capital of Zhejiang province, experts said such works involved risks, but not all are unavoidable.

"Such projects need very careful geological research and a detailed all-round risk evaluation before work starts, and construction must follow strict procedures," Shen Jingyan, the chief engineer of Subway and Railway Research Center, the Ministry of Construction, said.

"Authorities must improve management, and quality should not be compromised in trying to complete the projects in record time," Shen said.

A builder's quality consciousness is critical for the long-term success of such projects.

China has embarked on a fast subway development, something no country has done on such a large scale.

About 40 cities are building or planning to add 3,000 km of railway tracks in urban areas, out of which 1,700 km will be laid and become operational in 15 cities by 2015, said a report of the State Council's Development Research Center, issued last week.

Zhang Mi, a professor with Beijing Jiaotong University, said companies carrying out subway construction projects should try to avoid major risks.

They should do all the necessary preliminary work, including three-dimensional digital mapping, before starting construction.

The experts said it was too early to say what caused the tunnel collapse in Hangzhou. Geological conditions and construction operations have to be studied properly before the cause can be identified.

Zhang said the authorities and contractors should conduct geological and hydrologic tests and consider all the underground pipelines to work out how best to build a subway structure.

He called for a detailed digitalized monitoring system during the construction process, saying a foolproof risk management mechanism should be put into place.

"Usually problems in subway construction can be discovered early because they do show advance signs. If the problems can be fixed in time many accidents can be prevented," Zhang said.

There is a lot of pressure on government departments that conduct research and design a project.

"It is rather impossible to prevent all accidents because a ground collapse can't be predicted. But all efforts should be made to minimize the risk of accidents," Zhang said.