A Japanese plane narrowly avoided disaster earlier this month when it plunged over the Pacific, almost turning upside down, the transport ministry said on Wednesday.

The All Nippon Airways (ANA) flight, with 117 passengers and crew on board, dived 1,900 metres in 30 seconds in the incident off the southern Shizuoka district on September 6.

The manoeuvre happened when the co-pilot, in trying to unlock the cockpit door for the captain who was returning from the toilet, mistook a command button for the cockpit door lock switch nearby.

The plane, which took off from Naha on Okinawa island in the south, later managed to touch down at Tokyo's Haneda airport safely.

Two crew members were slightly injured, while four passengers reported health problems following the incident.

Images from the flight recorder on the Boeing 737-700 showed the plane veered to the right and then sharply to the left, before dropping backwards.

The aircraft tipped more than 130 degrees to the left at one point, but the darkness outside meant many of those on board did not realise the craft had almost flipped over.

"The images are incredible. The plane found itself in an almost unimaginable position," a pilot told the NHK television channel after the footage was made public.

A senior ANA official apologised to travellers at a press conference on Wednesday.

"We are deeply sorry for causing anxiety to our passengers," he said.

The incident occurred at about 10:50 pm (13:50GMT) while the craft was making its way across the Pacific.

Japan's transport safety board has launched an inquiry.