Five construction workers are reported dead and two more people are missing after a bridge collapsed during work on a remote reef in Japan, according to the Japanese coastguard.

The workers were reinforcing shore protection on the disputed Okinotori islands when the bridge suddenly collapsed, according to the Japanese broadcaster NHK.

A coastguard official confirmed that 16 workers were at the site and nine of these were confirmed to be safe, leaving two people missing.

"The coastguard has dispatched two escort ships and two jets for the rescue operation," he said.

The Okinotori atoll is 1,700km (1,056 miles) south of Tokyo and is the southernmost point of Japan's territorial claims.

It stretches across an area of approximately 11 square kilometres but has been largely eroded by waves, hence the extra shore protection work by the construction workers.

China disputes the territorial integrity of the reef, saying that the archipelago is just a group of rocks that should not be included in Japan's exclusive economic zone, which stretches 200 nautical miles from its borders.

No further details on why the bridge collapsed were immediately available.