A Japanese astronaut has apologised for 'fake news' after suggesting he had grown 9cm taller since arriving on the International Space Station.

41-year-old Norishige Kanai arrived on the International Space Station on December 17th, and sparked headlines when he tweeted about a significant growth spurt over the last fortnight.

In Japanese language tweets translated by Reuters, Mr Kanai said: “My height’s been measured here in space and somehow, somehow, I’ve grown 9 cm! In only three weeks I’ve really shot up, something I haven’t seen since high school."

He went on to suggest he was 'a little worried' he wouldn't be able to fit in his seat of the Soyuz spacecraft when returning to Earth due to the unexpected height increase.

みなさま、おはようございます。今日は重大なご報告があります。

実は、宇宙にç€ã„てからの身体計測があったのですが、な、な、なんと、身長が9センチも伸びていたんです！
たった3週間でニョキニョキと。こんなの中高生のとき以æ¥ã§ã™ã€‚

帰りのソユーズの座席に体が収まるか、ちょっと心配です。

— 金井 宣茂 (@Astro_Kanai) January 8, 2018

Most astronauts do in fact grow slightly taller when in space, as the spine's vertebrae spread apart in a low gravity environment. Their height returns to normal after they arrive back on Earth.

9cm, however, would be considered a far more dramatic growth spurt than usual - with BBC reporting a typical change of around 2-5cm.

However, around a day after his initial tweets and amid significant interest back on Earth, the Japanese astronaut moved to clarify the details.

He said ISS Russian commander Anton Shkaplerov had expressed skepticism over the significant growth spurt - and a fresh measurement proved that he was in fact only 2cm taller than his Earth height. 

Mr Kanai later tweeted: “This mis-measurement appears to have become a big deal, so I must apologise for this terrible fake news.

“It appears I can fit on the Soyuz, so I‘m relieved," he added.

Mr Kanai is part of ISS Expedition 54/55, and is due to remain on board the station until April.

He has shared a number of photos during his time in space so far, including of the view above Japan:

日本の上空を通ることも、たびたびあるのですが、雲に覆われていたりして、写真撮影の機会が、なかなかありません。

先日、秋田県だけが雲間からのぞいているのに出くわしました。八郎潟や、鳥海山（だとæ€ã„ます）をしっかりと写真に収めることができました。 pic.twitter.com/zKE89TrkVG

— 金井 宣茂 (@Astro_Kanai) January 10, 2018