SINGAPORE — China is rapidly building coast guard ships, the vessels that China most commonly uses for patrols in the South China Sea, and in the last three years has increased the number of ships in that category 25 percent, a new report by the United States Navy says.

China has the world’s largest coast guard fleet, with more such ships than its neighbors Japan, Vietnam, Indonesia, Malaysia and the Philippines combined, the report shows.

The unclassified assessment of the Chinese Navy, the first in nine years by the United States Navy’s Office of Naval Intelligence, says the rapid modernization over the last 15 years is yielding dramatic results.

The Chinese Navy is “on track to dramatically increase its combat capability by 2020 through rapid acquisition and improved operational proficiency,” the report says.