MANILA, July 20 (Reuters) - The threat of China invading Taiwan is something U.S. military ally the Philippines is monitoring on a daily basis as part of Manila's contingency plans for possible conflict in the region, its defence chief said on Thursday.

"We really have to make an assessment whether such is likely or not," Defense Secretary Gilbert Teodoro told reporters.

"Nonetheless, we continue to plan on all contingencies not merely any flashpoint between China and Taiwan, but any contingency within the theatre," he added.

Of the five U.S. treaty allies in the Indo-Pacific - Australia, South Korea, Japan, the Philippines and Thailand - the Philippines is closest to Taiwan, with its northernmost islands just 190 km (118 miles) away.

A priority for the Philippines is the safety of the more than 100,000 of its nationals living and working in Taiwan.

Without providing specifics, Teodoro, said the contingency measures being discussed were "a multi-agency effort and not only a defence effort".

The Philippines has been a key defence partner for former colonial power the United States for decades, but moves this year to expand U.S. access to its bases have angered China, which has called that "stoking the fire" of regional tension.

The Philippines has granted access to four additional bases this year, some facing north towards Taiwan. The Philippines has repeatedly stressed it is not taking sides in the U.S.-China rivalry.

Philippine President Ferdinand Marcos Jr, who has sought closer ties with Washington, has said the U.S. access to those bases would be "useful" defensively if China attacked democratically governed Taiwan.

Washington and Beijing have sought to manage their differences lately to get strained ties on the right track, including keeping communication channels open.

"Hopefully, the engagements bilaterally between the United States and China leads to the diffusion of tensions in that theatre," said Teodoro.