A rail company in Japan has apologised after one of its trains departed... 20 seconds early!

Management on the Tsukuba Express line between Tokyo and Tsukuba said they "sincerely apologise for the inconvenience" caused after the 9.44.40am train pulled away at 9.44.20am.

In most of the world, public transport showing up early or later than the stipulated time is a daily occurrence, but not in Japan, which is known for its all-round efficiency.

The train's operator believed the foul-up was serious enough to warrant an apology.

"We deeply apologise for the severe inconvenience imposed upon our customers," the Metropolitan Intercity Railway Company said in a statement.

The train's conductor had not properly checked the train's timetable, the firm said, adding that the crew had been instructed to strictly follow procedure to prevent a recurrence.

Passengers who might have made the train had it left on time suffered little inconvenience: the next one arrived just four minutes later!

The country's Tokaido line, which runs from Tokyo to the city of Kobe, is by far the world's busiest and carries nearly 150 million passengers a year.