XI'AN - Five natural gas workers suffocated while installing pipes in a shaft valve in Northwest China's Shaanxi province, local authorities confirmed Tuesday.

The accident took place at about 3:00 pm on Monday at a glass-making company in Fufeng county, while the five workers from a local natural gas company were working in a shaft valve, a spokesman with the county government said.

Local police and work safety authorities are investigating the cause of the accident, he said.