Stock markets retreated Tuesday as tensions in Hong Kong, an economic crisis in Argentina, uncertainty over US-China trade talks and fears of a global slowdown combined into a menacing cocktail of worry.

"A burst of geopolitical risks across the globe is severely burning stock markets and fuelling risk aversion," said Lukman Otunuga at FXTM.

Weakness in Asian stock markets spilled first into Europe and from there into US markets which extended Monday's substantial losses at Tuesday's New York opening bell.

"The US-China trade standoff, aggressive easing from some central banks, worries about a no-deal Brexit, chatter that Germany is heading towards a recession, political uncertainty in Italy, the financial meltdown in Argentina, and the tensions in Hong Kong are all contributing to the poor economic climate," said David Madden, analyst at trading group CMC Markets UK.

Markets might have been able to digest the issues one by one, but investors were finding their accumulation hard to stomach, said Craig Erlam at OANDA. 

"It's easy to ignore these issues when they are few and far between but we seem to be speaking about a new potential problem on a regular basis," he said.

Hong Kong airport authorities on Tuesday suspended all check-ins as pro-democracy protesters blocked the facility.

The decision came after thousands of demonstrators flooded into the airport for the second day running and blocked passengers from reaching entrances to the departure area in both terminals.

Hong Kong's main shares index finished down more than two per cent Tuesday, while Shanghai lost 0.6 per cent.

Tokyo retreated more than one per cent as exporters were hit by a rush into the yen, seen as a safe-haven investment. Gold, seen also as a safe bet, continued to push above $1,500 an ounce. Oil prices steadied.

Emerging market currencies recovered from Monday's losses that came on the back of the shock win in an Argentina presidential primary election by populist centre-left candidate Alberto Fernandez over incumbent Mauricio Macri.

The news saw the country's peso dive 30 percent at one point and the stock market by even more.

OANDA Asia-Pacific senior market analyst Jeffrey Halley said "economic populism is alive and well in all corners of the globe -- a far more worrying development in the long-term than a US-China trade war".

Back in Europe, there was much concern at a surprisingly weak key survey out of Germany, by the ZEW institute, showing that confidence among investors hit its lowest ebb in almost eight years in August.

Analysts said a slowdown in powerhouse Germany would have repercussions across the eurozone.

"This highlights the continuing uncertainty hanging over the bloc, with sentiment indicators so far suggesting that a pick-up in GDP growth in the second half of 2019 is not on the cards," analysts at Oxford Economics said.

The pound was stable against the dollar after data showed Britain's unemployment rate has edged up to 3.9 percent and wages grew at the fastest pace in more than a decade.

"Sterling has found some very mild support from better wage data -- pay up by the most in 11 years makes for a good headline for sure, but the risk of no-deal Brexit ultimately weighs," said Neil Wilson, chief analyst at Markets.com

London - FTSE 100: DOWN 0.6 percent at 7,180.80 points

Frankfurt - DAX 30: DOWN 1.0 percent at 11,566.25

Paris - CAC 40: DOWN 0.6 percent at 5,281.22

EURO STOXX 50: DOWN 0.6 percent at 3,306.70

New York - Dow: DOWN 0.1 percent at 25,871.61

Hong Kong - Hang Seng: DOWN 2.1 percent at 25,281.30 (close)

Tokyo - Nikkei 225: DOWN 1.1 percent at 20,455.44 (close)

Shanghai - Composite: DOWN 0.6 percent at 2,797.26 (close)

Euro/dollar: DOWN at $1.1213 from $1.1217 at 2050 GMT

Pound/dollar: UP at $1.2079 from $1.2076

Euro/pound: DOWN at 92.83 pence from 92.84 pence

Dollar/yen: DOWN at 105.22 yen from 105.28 yen

Brent North Sea crude: DOWN 18 cents at $58.39 per barrel

West Texas Intermediate: DOWN 40 cents at $54.53 per barrel