Five Chinese research vessels, including ships used for space and missile tracking and underwater mapping, were active in the northwest Pacific last month, as the United States stepped up military exercises, data from a Guam-based group shows.
Rapid militarisation in the northern Pacific gets insufficient attention, said the Pacific Center for Island Security, adding that it makes island populations a potential target in any great-power conflict.
"If you look at the number of US and bilateral and multilateral exercises, there is a lot of activity," Leland Bettis, the director of the group that seeks to flag regional security risks, said in an interview.
"Is the fact that the Chinese are sending research vessels into this area to map what is effectively undersea battle space surprising? Probably not."
The centre's Melanesian Security Monitor, launched on Thursday, shows three Chinese research vessels, including the space and missile tracking ship Yuanwang 7, near the tiny Pacific island of Kiribati over the last month.
A Pacific Ocean neighbour of Hawaii with close ties to Beijing, Kiribati has a vast exclusive economic zone spanning 3.6 million square kilometres (1.4 million square miles).
Last year it expressed concern at China's test of an intercontinental missile that landed near its waters.
Two more Chinese research vessels travelled east of the US territory of Guam, near island states with US defence compacts, the Federated States of Micronesia and Marshall Islands, the monitor showed.
China's foreign ministry did not respond to a request for comment on the purpose of the Pacific research vessel activity. Kiribati did not respond to a request for comment.
Between August and November, the United States has held nine multilateral war drills near Guam with allies such as Australia, India, Japan and South Korea, the monitor showed.
The United States has military bases in Guam and Marshall Islands, and overflight rights and maritime access to three freely associated states, Palau, the Federated States of Micronesia, and the Marshall Islands.
"Thirty years ago the US presence in these places would have been a deterrent, today that makes us a target, as a result of modern technology," Bettis, who lives in Guam, said shortly before Thursday's launch.
The monitor's visuals also show the spread of the US military footprint across Micronesia, including upgraded wharves and airfields.
The project is funded by commercial donors, the Carnegie Corporation and the Sasakawa Peace Foundation.
(Reporting by Kirsty Needham in Sydney; Editing by Clarence Fernandez)