Vietnam's prime minister on Thursday ordered a swift investigation into a scaffolding collapse that killed 13 workers and injured dozens, while a unit of South Korea's Samsung Group involved in the construction project offered initial assistance to victims' families.

All the victims were Vietnamese subcontractors working on a seaport breakwater project in the Vung Ang economic zone in central Vietnam, about 400 kilometers (248 miles) south of the capital, Hanoi.

More than 40 workers were on the scaffolding for nearly an hour Wednesday when it shook twice, sending them running to an elevator before someone stopped them saying there was no problem, laborer Dinh Ninh Dan, 27, told The Associated Press by telephone.

"After 10 more minutes, the scaffolding, which was about 20 meters (65 feet) high, suddenly collapsed. I quickly grabbed an iron bar but fell free," Dan said from Ky Anh General Hospital in Ha Tinh province, where he was being treated for hip pain along with 19 others, 15 of them with serious injuries.

"People were screaming, calling for help from the rubble," said Dan. "I was very lucky to survive."

A total of 13 bodies were pulled from the rubble, said deputy provincial police chief Bui Dinh Quang. Earlier reports said 14 had died because one victim was counted twice, said police officer Nguyen Sy Quan.

Prime Minister Nguyen Tan Dung urged authorities to investigate the cause of the collapse and "deal with it in a serious manner" according to the law.

Samsung C&T Vietnam, a unit of South Korea's Samsung Group, promised to cooperate fully with the investigation and offered initial support of 30 million dong ($1,400) for the family of each victim, state-run newspaper Tien Phong reported.

The Son Duong seaport is part of the Vung Ang economic zone, where Taiwan's Formosa Plastics Corp. is building a multi-billion dollar steel complex.

The site was the scene of an anti-China riot last May that left three Chinese dead following Beijing's deployment of an oil rig in South China Sea waters also claimed by Vietnam.