A satellite image shows what appears to be the construction of a third Chinese aircraft carrier at the Jiangnan Shipyard in Shanghai, China April 17, 2019. Construction of China's first full-sized aircraft carrier is well under way, according to satellite images obtained and analysed by a U.S. think tank. CSIS/ChinaPower/Maxar Technologies 2019/Handout via REUTERS

A satellite image shows what appears to be the construction of a third Chinese aircraft carrier at the Jiangnan Shipyard in Shanghai, China April 17, 2019. China has not formally confirmed it is building a third carrier, despite recent hints in state media, and the timing and extent of its carrier programme remain state secrets. CSIS/ChinaPower/Maxar Technologies 2019/Handout via REUTERS

A satellite image shows what appears to be the construction of a third Chinese aircraft carrier at the Jiangnan Shipyard in Shanghai, China April 17, 2019. CSIS analyst Matthew Funaiole told Reuters that images taken late last year were inconclusive, but that now the work under way is clear. CSIS/ChinaPower/Maxar Technologies 2019/Handout via REUTERS

A satellite image shows what appears to be the construction of a third Chinese aircraft carrier at the Jiangnan Shipyard in Shanghai, China April 17, 2019. China's first two carriers are relatively small, with only up to 25 aircraft, less than half the number aboard U.S. carriers, and have jump ramps built into their bows CSIS/ChinaPower/Maxar Technologies 2019/Handout via REUTERS