Growing concerns about stock bubbles on Wall Street are sparking fears of a pullback, highlighted by the wild ride for shares such as GameStop Corp.

A flood of money supply, ultra-low or zero interest rates and Covid-19 vaccine rollouts have sparked a "buy everything" rally, helping world stocks add a whopping $33 trillion in value from their lows of last March.

Surges in share prices of some loss-making firms, red-hot public markets and amateur investors chasing stocks have drawn concern as the benchmark S&P 500 has gained more than 70% since March...