More than 21,600 hazardous bridges in China have been renovated in the past 12 years, and transportation authorities across the country are attaching more importance to this issue, said the Ministry of Transport.

"Bridge construction and safety is an issue of public concern and one of the key tasks of transport departments across the country," said a statement published on Tuesday on the ministry's website.

A total of 43.88 billion yuan ($7.05 billion), including 17 billion yuan from the ministry, was invested in the renovation of 21,610 hazardous bridges from 2001 to 2012, curbing the high incidence of bridge accidents, according to the statement.

By the end of 2011, China had nearly 689,000 bridges, with almost 58,000 being large or ultra-large. The length of these two categories accounts for 51.8 percent of the total length of China's bridges.

"With some bridges undergoing long-term, overburdened operation, we have been witnessing a high incidence of bridge accidents in our country," the ministry said.

"Overloaded vehicles or those carrying items, which may damage the road surface, have often been observed, making it increasingly difficult to maintain the safety of bridges."

A succession of high-profile bridge accidents in recent years has attracted a wave of attention and criticism from the public.

A truck containing around 600 large packages of fireworks exploded and blasted off part of a viaduct about 30 meters above the ground in Mianchi county, Henan province, on Feb 1, killing 10 people and injuring 11.

The ramp of the $300 million Yangmingtan Bridge in Harbin, Heilongjiang province, which was in use for less than a year, tilted to one side and crashed onto the pavement 30 meters below early on Aug 24, taking four trucks with it. The accident killed three and injured five.

Harbin authorities said later that overloading caused the collapse, but this explanation was challenged by some netizens who claimed that poor construction quality was behind the tragedy.

At least 37 bridges collapsed across the country from 2007 to 2012, killing more than 180 people and injuring at least 177, according to earlier reports.

A bridge engineering researcher at Beijing Jiaotong University, who wished to remain anonymous, said: "The major cause of the frequent occurrence of bridge accidents lies in the absence of strict supervision on construction and close ties between corrupt officials and contractors.

"China's design capabilities are pretty strong and reliable, and our engineers have accumulated rich experience in bridge design since the nation has built many bridges over the past three decades.

"We usually apply a high redundancy of load-bearing capacity that is around two to three times heavier than the weight the bridge is designed to hold, therefore, theoretically overload alone should never destroy a bridge," he said.

"However I've seen too many quality problems in the construction of many bridges and most of them were easily neglected due to poor supervision and inadequate quality inspection. Moreover, excessive subcontracting has also led to the embezzlement of construction funds, forcing workers to use inferior materials."

Other factors also contributed to the accidents, he said.

zhaolei@chinadaily.com.cn