North Korea test-fired a ballistic missile off its east coast towards Japan early on Wednesday, its neighbors said, just days before US-South Korea Joint Military drills which Pyongyang views as invasion rehearsals.

This is the second such test in less than a week.

"Our military detected at around 6:00 am (2100 GMT on Tuesday) a ballistic missile launched by North Korea from the Wonsan area towards the East Sea," Seoul's Joint Chiefs of Staff said in a message to reporters.

Japan's Defence Minister Shinjiro Koizumi called the launch a "threat to peace and security in our region," adding that Tokyo had lodged a strong protest with North Korea through diplomatic channels in Beijing.

"It's a serious problem that affects the safety of the Japanese people," he said at a press conference.