A worker's helmet is seen at the subway construction cave-in site in Xi'an, capital city of northwest China's Shaanxi Province on Sunday, August 2, 2009. [Photo: Liang Meng/CFP]

Firefighters used bare hands to retrieve two migrant workers trapped after a section of a subway station under construction in Xi'an collapsed on Sunday morning.

The two, who had been buried under 10 cubic meters of earth for over three hours, died later in hospital.

The accident occurred at 9:20am at the Sajinqiao section of subway line one, where an area over 20-meters-wide of the construction site gave way, trapping workers below.

China Railway NO.2 Engineering Group Co., Ltd., which is responsible for the section's construction, blamed continued rain and leaking sewage pipes for the collapse.

The cave-in became the fourth accident in subway construction in the capital city of northwest China's Shaanxi province in seven months, the Wenhui Daily reported.

A fire accident occurred at a line 2 construction site on December 30 last year. Luckily, the fire was extinguished one hour later and all 64 workers were evacuated safely.

Only 66 hours later, on January 2, another station on line 2 caught fire due to improper operation by workers. Then on May 26, a person suffered minor injuries from a fire during infrastructure work on line 1.

Following the third accident, the Xi'an Subway Construction Office, the department overseeing the subway projects, ordered the 21 construction companies to each hand in three million yuan as a production safety guarantee. The deposit will be confiscated if any further accidents occur due to negligence or other human factors from the construction and supervision parties.

However, the harsh measures and a series of penalties meted out apparently failed to stop more accidents.

The Xi'an Subway Construction Office has called for safety checks at all of its subway construction sites in the city.

The planned 25-kilometer long line 1 subway will serve as the city's east-west artery line once it is completed at a total cost of around 13 billion yuan (1.9 billion US dollars).