China quietly mobilized thousands of fishing boats twice in recent weeks to form massive floating barriers of at least 200 miles long, showing a new level of coordination that could give Beijing more ways to impose control in contested seas.

The two recent operations unfolded largely unnoticed. An analysis of ship-tracking data by The New York Times reveals the scale and complexity of the maneuvers for the first time.

Last week, about 1,400 Chinese vessels abruptly dropped their usual fishing activities or sailed out of their home ports and congregated in the East China Sea. By Jan. 11, they had assembled into a rectangle stretching more than 200 miles. The formation was so dense that some approaching cargo ships appeared to skirt around them or had to zigzag through, ship-tracking data showed.

Maritime and military experts said the maneuvers suggested that China was strengthening its maritime militia, which is made up of civilian fishing boats trained to join in military operations. They said the maneuvers show that Beijing can rapidly muster large numbers of the boats in disputed seas.

The Jan. 11 maneuver followed a similar operation last month, when about 2,000 Chinese fishing boats assembled in two long, parallel formations on Christmas Day in the East China Sea. Each stretched 290 miles long, about the distance from New York City to Buffalo, forming a reverse L shape, ship-position data indicates. The two gatherings, weeks apart in the same waters, suggested a coordinated effort, analysts said.

The unusual formations were spotted by Jason Wang, the chief operating officer of ingeniSPACE, a company that analyzes data, and were independently confirmed by The Times using ship-location data provided by Starboard Maritime Intelligence.

“I was thinking to myself, ‘This is not right’,” he said, describing his response when he spotted the fishing boats on Christmas Day. “I mean I’ve seen like a couple hundred — let’s say high hundreds,” he said, referring to Chinese boats he has previously tracked, “but nothing of this scale or of this distinctive formation.”

In a conflict or crisis, for instance over Taiwan, China could mobilize tens of thousands of civilian ships, including fishing boats, to clog sea lanes and complicate military and supply operations of its opponents.

Chinese fishing boats would be too small to effectively enforce a blockade. But they could possibly obstruct movement by American warships, said Lonnie Henley, a former U.S. intelligence officer who has studied China’s maritime militia.

The masses of the smaller boats could also act “as missile and torpedo decoys, overwhelming radars or drone sensors with too many targets,” said Thomas Shugart, a former U.S. naval officer now at the Center for a New American Security.

Analysts tracking the ships were struck by the scale of the maneuvers, even given China’s record of mobilizing civilian boats, which has involved anchoring boats for weeks on contested reefs, for instance, to project Beijing’s claims in territorial disputes.

“The sight of that many vessels operating in concert is staggering,” said Mark Douglas, an analyst at Starboard, a company with offices in New Zealand and the United States. Mr. Douglas said that he and his colleagues had “never seen a formation of this size and discipline before.”

“The level of coordination to get that many vessels into a formation like this is significant,” he said.

The assembled boats held relatively steady positions, rather than sailing in patterns typical of fishing, such as paths that loop or go back and forth, analysts said. The ship-location data draws on navigation signals broadcast by the vessels.

The operations appeared to mark a bold step in China’s efforts to train fishing boats to gather en masse, in order to impede or monitor other countries’ ships, or to help Beijing assert its territorial claims by establishing a perimeter, said Mr. Wang of ingeniSPACE.

“They’re scaling up, and that scaling indicates their ability to do better command and control of civilian ships,” he said.

The Chinese government has not said anything publicly about the fishing boats’ activities. The ship-signals data appeared to be reliable and not “spoofed” — that is, manipulated to create false impressions of the boats’ locations — Mr. Wang and Mr. Douglas both said.

Researchers at the Center for Strategic and International Studies in Washington, when approached by The Times with these findings, confirmed that they had observed the same packs of boats with their own ship-location analysis.

“They are almost certainly not fishing, and I can’t think of any explanation that isn’t state-directed,” Gregory Poling, the director of the Asia Maritime Transparency Initiative at C.S.I.S., wrote in emailed comments.

The fishing boats assembled in the East China Sea, near major shipping lanes that branch out from Shanghai, among the world’s busiest ports. Cargo ships crisscross the sea daily, including ones carrying Chinese exports to the United States.

These are maritime arteries that China would seek to control in a clash with the United States or its Asian allies, including in a possible crisis over Taiwan, the island-democracy that Beijing claims as its territory.

“My best guess is this was an exercise to see how the civilians would do if told to muster at scale in a future contingency, perhaps in support of quarantine, blockade, or other pressure tactics against Taiwan,” Mr. Poling wrote. A “quarantine” means a sea operation to seal off an area that is meant to fall short of an act of war.

The boat maneuvers in January took place shortly after Beijing held two days of military exercises around Taiwan, including practicing naval maneuvers to blockade the island. Beijing is also in a bitter dispute with Japan over its support for Taiwan.

The fishing boat operations could have been held to signal “opposition to Japan” or practice for possible confrontations with Japan or Taiwan, said Andrew S. Erickson, a professor at the U.S. Naval War College who studies China’s maritime activities. He noted that he spoke for himself, not for his college or the navy.

Japan’s Ministry of Defense and coast guard both declined to comment on the Chinese fishing boats, citing the need to protect their information-gathering capabilities.

Some of the fishing boats had taken part in previous maritime militia activities or belonged to fishing fleets known to be involved in militia activities, based on a scan of Chinese state media reports. China does not publish the names of most vessels in its maritime militia, making it difficult to identify the status of the boats involved.

But the tight coordination of the boats showed it was probably “an at-sea mobilization and exercise of maritime militia forces,” Professor Erickson said.

China has in recent years used maritime militia fishing boats in dozens or even hundreds to support its navy, sometimes by swarming, maneuvering dangerously close, and physically bumping other boats in disputes with other countries.

The recent massing of boats appeared to show that maritime militia units are becoming more organized and better equipped with navigation and communications technology.

“It does mark an improvement in their ability to marshal and control a large number of militia vessels,” said Mr. Henley, the former U.S. intelligence officer, who is now a non-resident senior fellow at the Foreign Policy Research Institute in Philadelphia. “That’s one of the main challenges to making the maritime militia a useful tool for either combat support or sovereignty protection.”

Choe Sang-Hun contributed reporting from Seoul and Javier C. Hernández and Kiuko Notoya contributed reporting from Tokyo.

Data source: Starboard Maritime Intelligence.

About the data: We analyzed automatic identification systems (AIS) data of ships that broadcast positions near the formation in the 24-hour periods of Dec. 25, 2025 and Jan. 11, 2026 that either follow China’s fishing ship naming convention or are registered as China-flagged fishing vessels. Ships do not always transmit information and may transmit incorrect information. The positions shown in maps are last known positions at the specific times.