Ballistic Missile: Is North Korea preparing for yet another adventure
The isolated state apparently failed with an attempted launch at the end of May, which marked the most recent in a series of setbacks for its ballistic weapons programme.
But the country, which has been regularly condemned and sanctioned by the United Nations for missile and nuclear tests, has shown no signs of giving up on a weapons programme whose ultimate goal is to develop a nuclear weapon that could target the US mainland.
Japanese media, including Kyodo News agency and public broadcaster NHK, cited unidentified sources as saying signs have been detected of a possible launch.
Kyodo said Japan's military had been ordered to intercept any missile or falling parts that might threaten Japanese territory.
North Korean missile or rocket launches have flown over Japanese territory in the past, and the government has deployed anti-missile batteries in Tokyo and other parts of the country in response.
Defence officials in Tokyo said they could not comment, citing the sensitivity of the matter, but did not deny the reports.
In April the North failed three times to test-fired a missile with an estimated range of anywhere between 2,500 and 4,000 kilometres (1,550 to 2,500 miles).
The three failures were seen as an embarrassment for the Pyongyang leadership, coming ahead of a rare ruling party congress in May that was meant to celebrate the country's achievements.