One chart shows the dramatic drop-off in ship tracking data from China. This could be a sign of a worsening global supply chain crisis.

• The number of AIS signals from ships in Chinese waters has plunged 85% in under a month.
• Shipping companies use the data for a range of purposes, including the planning of shipping routes.

Ships in Chinese waters have vanished from tracking systems the maritime industry uses, a development that could worsen the global supply chain crisis.

The Automatic Identification System (AIS) — which relies on ships to send data to stations along the coastline or via satellites — has witnessed a plunge in the signals it receives in recent weeks.

Data from market intelligence and valuations provider VesselsValue show the number of signals in Chinese waters plunging 85% in under a month — from more than 100,000 a day on October 28 to over 15,000 a day on November 17.

The steep decline comes after China Personal Information Protection Law came into effect on November 1. The new rules regulate how domestic and foreign organizations collect and export the country's data.

There are no specific guidelines on shipping data due to the new regulations, but some domestic providers in China have stopped providing information to foreign companies due to the law, Reuters reported earlier this month.

Shipping companies use the data for a wide range of purposes, including the planning of shipping routes, logistical operations and congestion analysis.

As these signals typically provide the greatest data coverage and insight into shipping in Chinese ports, the decline in this data could significantly impact ocean supply chain visibility across China, one of the world's major trading countries, said VesselsValue's head trade analyst Charlotte Cook in an email statement to Insider.

"The increased availability and volume of AIS data in recent years has become something the industry widely depends on, allowing shipping lines to predict vessel movements ahead of time, track seasonal trends and improve port efficiency," said Cook.

"Ultimately, the significant reductions we are seeing in the count of vessels signaling in China will reduce the ability to accurately monitor vessel activity, and this could have knock-on effects to already squeezed global supply chains," she added.

"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," Anastassis Touros, AIS network team leader at ship tracking and maritime intelligence MarineTraffic, told Reuters.