China's Nanji Islands.

The imagery, captured on 13 October 2014 by Airbus Defence and Space's Pleaides satellite, shows a heliport with 10 landing pads in the centre of Nanji Island, one of a group of islands that are part of Zhejiang province.

China's Nanji Islands.

The construction at Nanji was reported on 22 December 2014 by Japan's Kyodo News, citing unidentified Chinese sources.

A comparison with DigitalGlobe imagery captured in October 2013 shows that the helipads are new additions to the island, along with wind turbines that sit along a ridge on the island's southeast peninsula. In contrast to the media reports, there are no signs of an airstrip under construction, although existing radar and communications sites are clear from the imagery.

On 25 December the Chinese Ministry of National Defense reacted by describing the story as "pure media hype."

"Some media in Japan make irresponsible speculations about China's legitimate activities and construction and play up tensions in the region. It is pure media hype," MND spokesperson Yang Yujun told a regular press conference.

Bases on the Nanji islands would be among the closest Chinese facilities to the Senkaku/Diaoyu islands but are still twice the distance of the nearest inhabited Japanese island of Ishigakijima, which is about 150 km south of the disputed islands.