China’s largest offshore oil producer Cnooc has started its first deep sea drilling project in the South China Sea, a move analysts see as a response to domestic pressure on Beijing to assert its claims in the disputed area.

Cnooc 981, China’s first self-developed deep sea drilling platform, started work in a spot 320km south-east of Hong Kong yesterday, the company said, adding it was planning to drill three wells and was optimistic that it would find oil.

It is unclear whether the platform’s location, in a block Cnooc calls Liwan 6-1, is in disputed waters. Li Jinming, a South China Sea expert at Xiamen University, said it was located between the Paracel Islands – an archipelago claimed by both China and Vietnam – and the Macclesfield Bank, claimed by China and Taiwan.