HANOI: Six Vietnamese workers were killed when a gas cylinder exploded at the construction site of a hydropower plant in central Laos, Vietnam's state media reported Saturday. The blast, which also injured two Vietnamese workers, occurred Friday night at the Nam Ngiep plant in Laos' central Bolikhamxay province, according to state-controlled VnExpress news site. The precise cause of the incident is still under investigation. But construction worker Truong Van Long told VnExpress a gas cylinder suddenly erupted at the site where the eight were working. "We are verifying the final number of casualties of the incident," a border official in Vietnam's Ha Tinh province told AFP, speaking on condition of anonymity. Construction on the 290-megawatt hydropower plant, which will consist of two dams and two power stations, began in 2014, forcing the resettlement of at least 4,000 villagers, mostly ethnic Hmong. It is one of nearly a dozen dam projects planned or under construction in Laos, a opaque and poor communist country that exports most of its hydropower energy to neighbouring countries like Thailand. Environmental groups strongly oppose the stoppages, which they say wreak havoc on local ecosystems and communities. Vietnamese state media reported that the bodies of the dead workers would be brought back to Vietnam for burial, while two injured workers are currently hospitalised in Laos. The group worked for a Vietnamese firm contracted to carry out construction on the hydropower project, which is funded jointly by Japanese, Thai and Laos partners. The Vietnamese construction company, Song Da 5, declined to comment on the incident when contacted by AFP.