A day after Nancy Pelosi’s trip, China has begun military drills near Taiwan. They appear to be designed as a trial run for sealing off the island. Five landed in Japanese waters.

At least 11 Chinese missiles struck seas north, south and east of Taiwan on Thursday, less than 24 hours after Speaker Nancy Pelosi celebrated the island as a bulwark of democracy next to autocratic China. The People’s Liberation Army declared its missiles “all precisely hit their targets,” even as Japan said five landed in its waters.

The Chinese military called the exercises a prelude to a bigger show of force intended to punish the island for a visit by Ms. Pelosi that challenged Beijing’s claims to Taiwan. The drills, pushing ever closer to Taiwan and expected to run 72 hours, will also give Chinese forces valuable practice should they one day be ordered to encircle and attack the island.

China’s top leader, Xi Jinping, has said that he hopes to eventually unify Taiwan and China through peaceful steps, as part of his vision for a “rejuvenated” and powerful nation. But like his predecessors, he has not ruled out force, and China’s military buildup has reached a point where some commanders and analysts think an invasion is an increasingly plausible, though still highly risky, scenario.

Even if imminent conflict is unlikely, the exercises are putting the region on edge. And tensions could dangerously escalate, especially if something goes wrong, with the missiles landing near Japan seen as a message that China could hit the U.S. forces stationed there and intended as a warning to the government in Tokyo of the cost of its American alliance.

The Japanese government on Thursday said that five Chinese ballistic missiles had fallen into its exclusive economic zone, the first time any had landed in those waters.

Another missile, the government said, landed 50 miles northwest of Yonaguni, a small island at Japan’s southernmost tip and just a short distance from Taiwan; the missile did not land in Japan’s economic zone.