The ministry is investigating eyewitness accounts that the main rotor detached midair causing the chopper to nosedive into a residential house in Kanzaki City, Saga Prefecture, with the ensuing fire rapidly gutting the house.

According to Japan's Defense Minister Itsunori Onodera, the AH-64D helicopter was on a test flight after having its main rotor head replaced.

The rotors on AH-64D attack choppers need their main rotor heads, which connect the four blades, replacing after 1,750 hours of flight time, Onodera said.

The four-blade, twin-turboshaft attack chopper had also undergone a routine 50-hour inspection.

The chopper took off from the the GSDF's Metabaru Camp located about 4 km from the crash site at 4:35 p.m. local time on Monday and is believed to have crashed into the house during its flight from east to west at 4:43 p.m.

All four residents in the two-story house that was hit by the chopper have been confirmed safe, although an an 11-year-old girl sustained minor injuries when she fled from her home.