Cambodia on Friday gave the green light to construction of its first oil refinery, a multi-billion-dollar Chinese-backed project, as the kingdom looks to tap its untouched offshore reserves.

Cambodia's oil and gas regulator approved a deal to allow SINOMACH China Perfect Machinery Industry Corp. and Cambodian Petrochemical Co. jointly invest $2.3 billion in the plant in the southwest of the country.

"We hope that we will have an oil refinery plant that can produce five million tonnes of oil products a year," Deputy Prime Minister Sok An said during the signing ceremony.

The plant is expected to start operating in late 2015.

Impoverished Cambodia had hoped to begin pumping oil this month from offshore fields, but the start has been delayed indefinitely, according to government officials.

The country was feted as Southeast Asia's next petro-state after oil was discovered there in 2005, but production stalled amid apparent wrangling between the government and US energy giant Chevron over revenue sharing.

"We have been trying our best to develop the oil sector for years but without results," Sok An said, adding that the government was still in talks with Chevron.

Cambodia could be sitting on hundreds of millions of barrels of crude and natural gas, according to some estimates, but it remains unclear how much can actually be recovered.