NASA astronaut Scott Kelly has tweeted images of the first flower to be grown in space.

Vibrant images of the International Space Stations's latest guest, an orange zinnia flower, were posted by Mr Kelly on Twitter.

"First ever flower grown in space makes its debut," he tweeted.

"Yes, there are other life forms in space!"

The astronaut, who posted mesmerising, colour-enhanced images of Australia from space in October, has been nursing the flowers since fellow crew member astronaut Kjell Lindgren returned to Earth in December.

At that stage the flowers were not holding up well to conditions on the Soyuz TMA-16M.

Mr Kelly became the 'autonomous gardner' aboard the space station, and was given one page of care instructions to assist the rescue mission.

On December 28, Mr Kelly tweeted a picture of the flowers in distress.

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After tending to the plants over the holiday period, two zinnia plants died, and the remaining two continued to thrive.

On January 8, Mr Kelly posted an image of the impressive turnaround and tiny buds beginning to sprout.

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NASA said the zinnia flower was chosen because it can help scientists understand how plants flower and grow in microgravity, not for its beauty.

The space agency said growing flowering crop is more challenging than vegetative crop, and the issues faced by Mr Kelly presented a good learning opportunity for scientists.