Asset prices have risen dramatically during the last six months, much like housing prices appreciated during the last decade, raising alarms that a crash could be coming in the equities market, writes economist Robert Samuelson.

Writing in Newsweek, Samuelson reckons that since March 9 the U.S. stock market has climbed by more than 50 percent. This is nothing short of a speculative frenzy, not based on underlying economic fundamentals, he says.

“An index of stocks for 22 emerging market countries — including Brazil, China and India — has doubled from its recent low. Oil at about $80 a barrel has increased 150 percent from its recent low of $31,” he writes.

“Gold is near an all-time high around $1,090 an ounce. Meanwhile, the dollar has dropped against many currencies. Haven't we seen this movie before?”

There now appears to be a thin line between maintaining a sound economic expansion and cultivating bubbles.

“With hindsight, lax Fed policies contributed to both the ‘tech’ bubble of the late 1990s and the recent housing bubble, though how much is debated,” writes Samuelson.

“How deftly the Fed navigates from its present policy matters for the world as well as the United States. If it's too fast, it may kill the economic recovery; if it's too slow, it may spawn bubbles — and kill the recovery.”

Around the world, economists concur.

Bloomberg News reports that Brazil’s real is now deemed overvalued, and the stock market in Brazil is soaring based on economic growth figures in China — trends that are not exactly rational.

NYU economist Nouriel Roubini has also argued that Brazil’s stock market is overheating in recent weeks.