A US submarine arrived in South Korea on Tuesday as it prepares to join an "armada" of warships sent to the region by Donald Trump to confront Pyongyang.

The nuclear-powered USS Michigan, which is built to carry and launch ballistic missiles and Tomahawk cruise missiles, made the port call amid growing concerns that North Korea was set to carry out a nuclear test.

Kim Jong-un’s regime marks the 85th anniversary on Tuesday of the founding of its Korean People's Army – a symbolic date which observers believe could see a test of military hardware.

Such concerns eased during the afternoon, with no reports of tests, but South Korean media said the North was carrying out its “largest-ever live-fire drills” to mark the occasion.