Four workers are missing and presumed to have drowned after the partial collapse of a dam being constructed in western Cambodia, officials have said.

Major Theang Leng, chief of police in the district where the hydroelectric dam is located on the Atay River, said on Sunday that the collapse 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 had been halted as experts surveyed the damage.

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

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

In a 2008 report, the US-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 $255m 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.

Source: AP