While Europe's leaders were wrestling with the problem of who will bail out whom last week, the world's other two major trading blocs, the US and China, were gearing up for a potentially damaging trade war.

As China slapped punitive import taxes on gas-guzzling American cars, and stepped up its rhetoric against the US, complaining about what it said were US subsidies, some Beijing-watchers read it as a sign that the government is so alarmed about a looming economic slowdown that it is casting around for someone to blame.

The tariffs, ranging from 2% to 21.5%, will be levied on imports of SUVs and cars with engines of 2.5 litres or more, hitting the US car giants.

It's not hard to see why China is lashing out. Evidence is mounting that just a few months after Beijing was fretting about its economy overheating and taking action to tame rampant food prices, the most pressing concern now is a so-called hard landing.

Foreign investment in China was almost 10% down in November on a year earlier – the first such decline since 2009. HSBC's purchasing managers index, which tests the strength of the manufacturing sector, is pointing to a contraction in the fourth quarter. And Beijing was forced to spend some of its vast foreign exchange reserves in October buying up yuan to prevent the currency falling too far.

Alarming tales are emerging of social unrest, too. People in Wukan, in Guangdong province, have been protesting about collusion between developers and local government.

A year ago, all the talk was of China overheating as cheap US capital poured in. Beijing unleashed several measures, including raising reserve requirements for its banks and intervening to limit price rises for agricultural products, to prevent a credit boom from running out of control. But it failed to anticipate the coming eurozone slump.

"What's difficult to disentangle is how much of the slowdown in emerging markets is because China tightened policy," says Karen Ward, senior global economist at HSBC. "If it had known what was going to happen in the developed world, it might not have been so tough."

Commerce ministry spokesman Shen Danyang warned last week that "the overall trade environment next year will be complicated, partly due to the economic uncertainties in [Europe], and... the export situation in the first quarter will be very severe". Another danger signal is that the cost of shipping goods from China to Europe has dropped by an extraordinary 39% since August as demand has fallen away, according to Clarkson Securities.

Graham Turner of GFC Economics, who has studied Japan's "lost decade" of stagnation and recession, sees parallels between today's China and Tokyo's efforts to engineer a soft landing in 1990 by bringing exploding property prices under control. "It absolutely is where Japan went wrong: it tried to deflate the property bubble and it just went too far."

Michael Derks, chief strategist at foreign exchange broker FxPro, points out that credit has expanded rapidly in recent years, with the ratio of loans to GDP doubling since 2006, as Beijing encouraged borrowing to maintain demand in the face of the global slowdown in 2008 and 2009.

Chinese property prices have been falling sharply in recent weeks and there have been reports of "kerbside lenders" in the black market going bust, and hard-up business owners fleeing town to escape bailiffs.

Turner says these informal lenders in the so-called shadow banking system can be a crucial source of credit, and if the sector is collapsing, the economy could shudder to a halt. The People's Bank of China has already signalled it is switching from reining in the economy to boosting growth; he says it will have to act fast.

But not everyone is concerned about a "hard landing". Ward says China still desperately needs more infrastructure investment: "Forty per cent of people still work in fields: how can you think there's overcapacity?" She also says China has $3tn of foreign currency reserves to insulate itself against the west's travails. It could also allow the yuan to depreciate against the dollar.

As the frenzy of the euro crisis wanes, many analysts believe the eyes of the world will turn east in the new year – but it's impossible to predict what will happen next. As Turner puts it: "People can claim that it's going to go one way or another but, in reality, nobody knows."