You can add London Telegraph columnist Liam Halligan to the list of experts who see China's devaluation of the yuan last week as a sign of its entry into the global currency war.

The yuan has slid 3 percent since the government's move last Tuesday. The dollar traded at 6.3926 yuan Tuesday, up from 6.2086 yuan a week ago Monday.

"Beijing, while it has an eye on the IMF’s decision on SDRs, is firing back a currency war salvo," Halligan writes.

He was referring to China freeing its currency market to convince the IMF to include the yuan in its special drawing right unit, which would help the yuan become a reserve currency.

But Halligan sees trouble for the Asian titan ahead.

"China has massively over-invested, the banking sector is full of non-performing loans, stock valuations remain bloated and many companies have borrowed heavily overseas," he notes.

"If the Chinese central bank is concerned enough to yank down the currency, making those foreign loans even bigger, maybe it is time for us to worry."

China's economy officially grew 7 percent in the second quarter, conveniently matching the government's target. But economists say that number is vastly overstated and that 3 to 5 percent would be more accurate.

Meanwhile, Ruchir Sharma, head of emerging markets and global macro at Morgan Stanley Investment Management, worries about China pulling down the world economy.

"Over the past 50 years there has been a global recession once every eight years, on average, so the next one may be brewing,"he writes in The Wall Street Journal. "The policy panic in Beijing over its currency and the fall of its stock market suggest that the next global recession likely will be 'made in China.'"

The Shanghai Stock Index has dropped 27 percent since June 12.

The U.S. economy used to be the prime cause of global recessions. But since 2010, China has accounted for one-third of global growth, compared to 17 percent for the U.S., Sharma explains.

"The world is one shock away from recession," he writes. "A debt-laden China is now the critical link, and another one- or two-percentage point decline in its growth rate could provide that shock."

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