PHNOM PENH, Cambodia (AP) — Four workers are missing and presumed to have drowned after the partial collapse of a dam being constructed in western Cambodia, officials said Sunday.

Maj. Theang Leng, chief of police in the district where the hydroelectric dam is located on the Atay river, said the collapse Saturday appeared to have occurred because the dam was holding too much water and had started leaking. A search was under way for the missing workers. Four other workers were seriously injured.

Theang Leng said construction work was halted as experts survey the damage.

Cambodia has an electricity shortage. Some hydroelectric dams under construction have been criticized because of their environmental and social impact.

Yeat Thay, who lives near the dam, said the reservoir was completely emptied by the accident. He said there were rumors that three to five Chinese experts involved in the construction were also missing, but Theang Leng denied this.

In a 2008 report, the U.S.-based watchdog group International Rivers Network said "poorly conceived hydropower development could irreparably damage" Cambodia's environment and also extract a social cost. In addition to being displaced, villagers are also often deprived of the natural resources they use to make a living.

Work on the 120-megawatt Atay hydroelectric project began in 2008 and had been scheduled to be finished in May 2013. The $255 million project is being undertaken by the China Datang Corp. as a build-operate-transfer concession under which the company will operate it for 30 years.

A man who answered the phone at Datang's duty office in China said he had no information about the incident and refused to provide a number for a company spokesman.

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Associated Press writer Christopher Bodeen in Beijing contributed to this report.