A section of a bridge under construction in southern Vietnam collapsed Wednesday, killing at least 52 workers and injuring 97 others, officials said.

The bridge was being built across the Hau River, a branch of the Mekong River, in the southern city of Can Tho. It is part of a heavily used route linking the Mekong Delta and Ho Chi Minh City.

The collapsed section was more than 98 feet tall and was situated above land on the river bank in Vinh Long province, said Vo Thanh Tong, chairman of the Can Tho people's committee. The four-lane bridge was not yet open to traffic.

Images broadcast on Vietnamese television showed mounds of twisted steel and cables shrouded in dust and smoke. Dozens of workers in yellow helmets rushed about the wreckage, some carrying stretchers with bloody victims.

At least 52 people were dead and 97 others were injured, said Le Van Ut, the vice chief of police in Vinh Long Province. The exact number of missing was unknown, but officials at least 200 people were working on the 328-foot-long section when it buckled at about 8 a.m.

"I expect the death toll to rise, as there still victims trapped under the concrete," said Dang Van Tam, director of Central Can Tho General Hospital.

Local hospitals were overwhelmed and had called in 20 surgeons from Ho Chi Minh City to help. "We have never had this many patients," Tam said.

Le Viet Hung, vice chief of the Can Tho police, said the scene was "total chaos."

"It sounded like a huge explosion," Hung said. "It's the biggest accident I've ever seen."

The 1.7 mile bridge was started in 2004 and expected to be finished next year. It was to be the largest suspension bridge in Vietnam and would greatly speed the trip across the river, which thousands now make daily by ferry.

Officials were still investigating the cause of the accident. Cement had been poured into the collapsed section just one day earlier, on Tuesday. The bracing supporting it had apparently weakened, said Pham Van Dau, chairman of the Vinh Long people's committee.

Japan provided a $218 million loan to finance the project, enough to cover 85 percent of the cost, said Yoshifumi Omura, of the Japanese Bank for International Cooperation in Hanoi. The Vietnamese government provided the rest of the funding.