China's customs authority has dropped Panama from the list of flag states that enjoy privileged status and low port dues, according to several sources.

Panama's ship registry is popular among Chinese state-owned enterprises (SOEs) and private shipowners.

"In today's markets, where most owners no longer have to count every penny, I wouldn't expect many people to do much about it," said one shipowner with Panama-flagged vessels, who was not willing to be identified.