The roof of a five-story cement factory under construction in Bangladesh collapsed Thursday, killing at least four workers and trapping many others, an official said.

About 150 workers were on duty when the collapse occurred at Mongla in Bagerhat district, fire official Mizanur Rahman said.

He said at least 30 people were rescued from under the debris and up to 40 were feared trapped. Many of the survivors were injured and were hospitalized, Rahman said.

The cause of the collapse was under investigation.

The factory, about 135 kilometers (85 miles) southwest of Dhaka, was owned by an army welfare organization, the United News of Bangladesh news agency reported.

In April 2013, a building housing garment factories collapsed in Dhaka, killing more than 1,100 people. Engineering surveys show that many Bangladesh factories violate building codes by using substandard materials or adding floors that the building foundations can't support.

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http://www.miamiherald.com/news/nation-world/article13744295.html#storylink=cpy