Three people were killed in a bridge collapse in Harbin on Friday, renewing worries over the quality of Chinese infrastructure amid a construction boom across the nation.

The bridge - which cost $300 million and was in use for less than a year - was at least the sixth bridge to collapse in little more than a year in China.

The ramp, about 3.5 km from the main span of the Yangmingtan Bridge, tilted to one side and crashed to the ground at 5:32 am, plunging four trucks to the pavement below, Huang Yusheng, a spokesman for the government of Harbin, Heilongjiang province, said at a news conference on Friday.

The collapsed ramp, some 100 meters in length, fell from a height of 30 meters, according to Xinhua News Agency.

Two people were killed on the spot, a third died later, and five remain in hospital, Huang said.

The four trucks appeared to be overloaded with stone and feed, Huang told reporters.

The bridge, part of an airport expressway in Harbin, opened in November after 18 months of construction, local media reported. The bridge was designed to handle up to 9,800 vehicles an hour.

Investigations are under way.

But Huang Yi, spokesman for the State Administration of Work Safety, China's top safety watchdog, said that there must be some quality problems with the bridge.

"We will urge local authorities to release the investigation results in a timely manner," he told a news conference in Beijing on Friday.

Eyewitnesses were shocked by the accident.

"I heard a deafening sound when I was washing my face," said a construction worker who only gave his surname as Wang. "The prefabricated house I was staying in shook like it was an earthquake."

Wang's fellow worker said he was piloting a crane with his back facing the bridge. "I turned back after hearing the thud and saw one truck had already crashed upside down on the ground and three others rolled over," said the man, who didn't give his name.

Among the injured, one is female, according to Sun Ran, deputy head of Harbin No 1 Hospital.

"Three people were seriously injured and they need immediate operations," she said.

Sun said the most seriously injured is Feng Licheng, a 41-year-old man whose liver was lacerated and vertebra broken and there are some wounds on his head.

"All the injured are out of life-threatening danger except Feng," Sun said.

It was at least the sixth major bridge collapse across the country since July last year and shoddy construction and overloading are to blame, according to Xinhua.

Contact the writers at chenxin1@chinadaily.com.cn and zhaoyunpeng@chinadaily.com.cn

Tian Xuefei in Harbin contributed to this story.