I've been hearing that since the 1990's when it first started to become apparent that their economy was on track to overtake the rest of the world within a few decades.
It hasn't happened yet. Is there something you perceive as especially problematic now, as opposed to the last 30 years?
I've never once heard it from somebody who correctly anticipated China's rise though. The imminent collapse story just quietly changes every 5 years or so.
If the US has an imperial rival one thing you can almost guarantee is that the predictions of economic collapse will be as frequent as they are absurdly overblown and as always, This Time It's Different.