Sky News Senior Reporter Caroline Marcus has commented on US President Joe Biden's hot mic moment at the Quad Summit.

Biden met with Prime Minister Anthony Albanese at his home in Delaware on the weekend where hot mics picked up the leader of the free world telling Mr Albanese and Japan's Prime Minister Fumio Kishida an "aggressive" China was "testing" the US and its allies.

“The first thing that always strikes me with these stories is they know how microphones work, don't they?” Ms Marcus said.

“I mean, they've been around a few as the presidents and leaders of various countries. And yet we see time and time again that they just don't seem to understand that microphones pick up sound.

“Of course, they're concerned about China and they've just been carrying on with this pretence that the court is not actually about containing China and managing its aggression and now, as you say, the cat's out of the bag.”