North Korea fired three ballistic missiles into the Sea of Japan on Thursday, the Defense Ministry in Tokyo said, in an apparent show of strength after the isolated country reported for the first time a COVID-19 outbreak.

The launches were the latest in a record-breaking series of weapons tests this year and came ahead of a planned visit to South Korea and Japan next week by U.S. President Joe Biden.

The Defense Ministry said the three short-range missiles had hit a maximum altitude of about 100 kilometers, traveling about 350 km before falling into waters outside Japan’s exclusive economic zone, which extends 200 nautical miles (370 km) from its coast.

South Korea’s military also confirmed the launches, saying the missiles were fired from the Sunan area of Pyongyang, where an international airport is located and where the North claimed to have fired its largest intercontinental ballistic missile (ICBM), the Hwasong-17, on March 24.

Earlier Thursday, North Korean state-run media reported that the country had declared a "gravest national emergency," with leader Kim Jong Un ordering a national lockdown.

Kim, seen wearing a mask for the first time in state-run media, oversaw an emergency politburo meeting to discuss the outbreak and "called on all the cities and counties of the whole country to thoroughly lock down their areas."

The latest launches come just two days after conservative South Korean President Yoon Suk-yeol took office. Yoon has signaled a harder line on the North's nuclear and missile programs than his predecessor, though he did extend an olive branch in his inauguration speech, offering up an “audacious” plan for economic aid — but only on the condition that Pyongyang first give up its nuclear arsenal.

Thursday’s launches also come ahead of Biden’s May 20-24 trip to South Korea and then to Japan, where North Korea is expected to be near the top of the agenda in talks with Yoon in Seoul and Prime Minister Fumio Kishida.

Leif-Eric Easley, a professor at Ewha University in Seoul, said that the latest missile firings appeared excessive to what would be needed to test and improve military capabilities.

“These launches look like a show of strength after the Kim regime publicly admitted to a coronavirus outbreak,” Easley said. “Despite the new South Korean administration’s expressed willingness for dialogue, engagement won’t be easy because even international humanitarian assistance will have to navigate Pyongyang’s political pathologies.”

In its last weapons test on Saturday, the North was believed to have fired off a submarine-launched ballistic missile as it seeks to further diversify its arsenal. Many of the missile launches this year have been of weapons designed to evade missile defenses, including a test on April 16 of what the North said was a new guided system apparently intended to carry smaller “tactical nukes.”

Kim has vowed to double down on further developing his nuclear and missile programs, warning late last month that Pyongyang could “pre-emptively” use its nuclear weapons to counter hostile forces, days after delivering a fiery speech at a rare large-scale military parade that showcased the country’s increasingly advanced arsenal.

U.S. and South Korean officials have also said that the North could soon oversee an underground nuclear test for the first time since 2017, when it tested what it said was a thermonuclear bomb, possibly as early as this month.