MANILA - China is nearly done building air and naval facilities on seven islands it claims in the South China Sea, recent surveillance photos obtained by a Philippine newspaper and published yesterday showed.

Responding to the report, President Rodrigo Duterte's spokesman Harry Roque said the government was monitoring the situation and would continue to maintain good ties with Beijing.

"Right now, the posture of the President is maintain close ties so they wouldn't have any reason to use those arms in those islands."

The photos, taken from June to December last year and obtained by The Philippine Daily Inquirer, show that the runways for the three biggest islands - Fiery Cross, Subi and Mischief - have been completed or are ready for use.

Lighthouses, radar domes, hangars and multi-storey buildings have been built on them, while helipads, wind turbines and observation and communication towers can be seen on four smaller islands - Burgos, Calderon, McKennan and Johnson South.

The Asia Maritime Transparency Initiative, a US think tank, said most of the work had been done on Fiery Cross, which now has a 3km long runway and at least one rocket weapons system. It also reported underground tunnels, missile shelters, radars and high-frequency antennas on the islands.

The seven islands, which are also claimed by the Philippines, are shaping up as air and naval bases with few features for purely civilian uses, the Inquirer said.

Its exclusive report comes amid concern among some quarters in the Philippines that growing economic ties with China have led to the Duterte administration downplaying Manila's territorial claims.

Mr Roque said there was little the Philippines could do, short of declaring war, and that the reclamation and military build-up started while Mr Duterte's predecessor Benigno Aquino was in office. Diplomatic protests and a case lodged by the Philippines before an international tribunal failed to stop China, he added.

"What else can be done? We'll continue relying not only on good faith," Mr Roque said. "We expect that China, being not just a member of the United Nations but also a permanent member of the Security Council, will adhere to the prohibition on the use of force."

Observers have suggested that China embarked on its massive island-building programme in response to the case filed by the Philippines in January 2013 challenging China's claims to nearly all of the South China Sea.

In July 2016, an arbitral tribunal in The Hague ruled in the Philippines' favour and nullified China's claims.

By then, China, which refused to recognise the ruling, had already transformed seven small reefs it had been occupying into islands, in a pointed effort to stake its claims.

Some of Beijing's claims also overlap with those of Brunei, Malaysia and Vietnam, and Asean members are set to start talks with China on a code of conduct to manage tensions in the disputed waters.

A senior diplomat, who spoke on condition of anonymity, said China's military build-up was "understandable" considering recent talk of military alliances in the Indo-Pacific region.

Observers also feel South-east Asia should engage China to help maintain regional security and find ways to cooperate.

But Senator Paolo Benigno Aquino expressed alarm over the Inquirer's report.

"It's disturbing knowing China's military bases in the South China Sea are nearly completed," he said. "While their warships are in our seas, we continue to give in to their whims and, all the while, we are kept in the dark as to our government's dealings with China."