Five ballistic missiles launched by China's military during exercises around Taiwan on Thursday were believed to have landed inside Japan's exclusive economic zone for the first time, Defense Minister Nobuo Kishi said.

The Defense Ministry said all five of the missiles that landed within Japan's EEZ — which extends 200 nautical miles (370 kilometers) from Japan's coast — had fallen into waters southwest of Hateruma Island in Okinawa Prefecture.

Kishi said the Japanese government delivered a diplomatic protest to Beijing over the move.

"This is a grave issue that concerns our country's national security and people's safety," Kishi told a hastily organized news conference.

The defense chief said the Chinese military had launched nine ballistic missiles, though China's Defense Ministry said earlier Thursday that it had fired off 11 ballistic missiles into waters to the north, east and south of Taiwan. Taiwan's Defense Ministry also confirmed 11 launches. The reason for the discrepancy was not immediately clear.

The Japanese Defense Ministry said that four of the weapons were believed to have flown over Taipei before landing in Japan's EEZ — a move that would be seen as a major escalation by Beijing.

China announced late Tuesday that it would hold some of its largest-scale military exercises, including ballistic missile launches, in response to a visit to self-ruled Taiwan by U.S. House Speaker Nancy Pelosi.

Pelosi, who is leading a congressional delegation on a multicounty tour of Asia, landed in Japan — the last leg of the trip — later Thursday.

China, which considers democratic Taiwan an integral part of its territory that must be brought back into the fold, by force if necessary, claimed the visit by Pelosi represented yet another attempt at "hollowing out" the United States' long-standing “One China” policy. Under that policy, Washington officially recognizes Beijing rather than Taipei. The U.S., however, is also bound by the Taiwan Relations Act to provide the self-ruled island with the means to defend itself.

But while the latest Chinese missile drills are ostensibly focused on the U.S. and Taiwan, they're also a clear warning to Japan, experts say, with some of its far-flung southwestern islands sandwiched between the exercise zones, according to coordinates released by the Chinese military.

In Okinawa Prefecture, Yonaguni Island — located just 110 kilometers from Taiwan — as well and Miyako Island, are home to Ground Self-Defense Force bases, while construction is currently underway on another base for surface-to-air and surface-to-ship missile units on Ishigaki Island.

China has repeatedly sent warships and warplanes into that area in recent years as part of what it says are routine training operations. It also conducted military drills near Taiwan during what is known as the “Third Taiwan Strait Crisis” in 1995-96. But the drills announced late Tuesday encompass a far larger area than those exercises, and include large swaths to the northeast and east of Taiwan, where U.S. and Japanese forces would likely arrive from in the event they are deployed to aid Taipei following any Chinese invasion.

Senior Japanese officials, including late former Prime Minister Shinzo Abe, have said that a Chinese attack on democratic Taiwan — a key semiconductor-maker that sits astride crucial shipping lanes that provide Japan with much of its energy — would also represent an emergency for Tokyo.