North Korea started Thursday by launching three more missiles, including one that prompted emergency shelter orders in three Japanese prefectures.

Residents were warned to immediately take shelter indoors in Japan’s Miyagi, Yamagata and Niigata prefectures. Televisions in some parts of the country were interrupted by emergency alerts.

Japan’s emergency broadcast system initially said the North Korean missile flew over and past Japanese territory, but defense officials later retracted that claim and said they were investigating further.

South Korean media reported that the missile was likely an intermediate- or long-range missile. No other details were immediately available about the launch, which would have been the second time this month for a North Korean missile to overfly Japan.

About an hour after that missile launch Thursday, North Korea sent two more missiles toward the sea, according to alerts by South Korea’s military and Japan’s coast guard. No further details were available.

North Korea has launched at least 27 missiles, along with more than 100 rounds of artillery, since early Wednesday, as it continues to display its anger over ongoing U.S.-South Korea military drills.

North Korea aimed three of Wednesday’s launches toward South Korea, triggering alerts on televisions in the South and air raid sirens on an island off the coast.

One of the North Korean missiles fell into waters just 57 kilometers east of Sokcho, a coastal tourist city in South Korea’s northeast. Another missile landed 167 kilometers from Ulleung County, a sparsely populated island region off South Korea’s east coast. The third fell in international waters, 26 kilometers south of the de facto inter-Korean sea border.

Seoul’s response

In response, South Korea’s military said its warplanes launched three missiles north of the de facto sea border to demonstrate South Korea’s “capability and readiness to strike the enemy with precision.”

It is the first time since the end of the 1950-53 Korean War for either country to send missiles across the Northern Limit Line, according to South Korea’s Ministry of National Defense.

In response to the North’s Wednesday launches, South Korea’s transport ministry said it closed some air routes off its east coast until at least Thursday morning.

North Korea has fired more than 50 ballistic missiles this year — a record — but until Wednesday none had been launched toward South Korean territory or resulted in public air raid alerts.

The developments further raised tensions on the Korean Peninsula, where both sides have increased displays of military strength.

Lee Juhyun contributed to this report.