Beijing, Jan 5 China has begun working on its third aircraft carrier, a development reflective of its ambition to become a dominant sea power. The Hong Kong-based South China Morning Post has reported that work on the aircraft carrier began after March last year. The paper quoted a source saying that work was still on at the carrier's hull and will be finished in about two years. The source also said building the third carrier will be challenging than the other two. China last year launched its first home-grown aircraft carrier, which is likely to operate later this year. The one in service, Liaoning, was bought unfinished from the former USSR. The sources, according to the report, said it was too early to say about the launch of the third aircraft carrier. According to naval experts, China plans to have four aircraft carrier battle groups in service by 2030. With maritime disputes and tensions with several countries, China is rapidly building its navy. Beijing is locked in a dispute with five littoral states in the South China Sea while its claims to Senkaku islands are contested by Japan. Its submarines have been spotted in the Indian Ocean where China is flexing its muscles. China last year established its first overseas military base in Djibouti in the Horn of Africa. Another reason for China's naval buildup is to ensure the safety of the planned maritime route under the ambitious Belt and Road project. The project aims to connect Asia, Africa and Europe through a network of ports, sea lines, highways and railways. The second-most powerful navy after the US, China has some 65 submarines whereas India has 14. In comparison to China's 48 frigates, India has 14. Experts say China's Yuan-class diesel-electric submarine models are quieter than the American nuclear ones. However, China's overall naval strength is still far behind that of the US.