ATHENS' Marine Traffic, one of several online ship location trackers, now finds ship disappearing from its online maps, following the introduction of a new mainland data law, Reuters reports.

Ships in Chinese waters are disappearing from tracking systems that are impacted by China's November 1 Personal Information Protection Law designed to increase government control over how domestic and foreign organisations collect and export China's data.

Although there are no specific guidelines on shipping data in the regulations some domestic providers in China have stopped giving information to foreign companies as a direct consequence of the new rules, sources told Reuters.

The data is relied upon to provide information on cargo volumes and helps optimise logistics by predicting congestion so companies can make key decisions on shipping routes.

"If this continues, there will be a big impact in terms of global visibility especially as we come into the busy Christmas period with supply chains already facing huge problems all over the world," said Anastassis Touros, AIS network team leader at MarineTraffic.

"All of a sudden we do not know when ships are leaving and from where, and we also don't have the full picture on port congestion which AIS offers us."

The so-called Automatic Identification System (AIS) provides the location of ships. It is used by other vessels, ports, and many other organisations from banks and traders to search and rescue operations.

From October 28 to November 15 the level of terrestrial shipping data across all Chinese waters was estimated to have dropped 90 per cent according to market intelligence and valuations provider VesselsValue.

"With China being a major importer of coal and iron ore and one of the main container exporters globally, this decline in positional data could cause significant challenges concerning ocean supply chain visibility," head trade analyst Charlotte Cook said.

An official with the Guangdong Maritime Safety Administration told Reuters that AIS rules were set by the department's headquarters in Beijing. Calls to the Maritime Safety Administration's Beijing office were not answered.