An ugly start to European trading pushed world shares towards their lowest level in a year on Tuesday, as negative drivers from Saudi Arabia's diplomatic isolation to worries about Italy's finances and trade wars piled on the pressure.

Selling escalated from Wall Street into a heavy selloff in Asia before hitting Europe, which was facing a fifth day of uninterrupted declines.

The pan-European STOXX 600 was near a two-year low with almost half of its stocks now in bear-market territory — down 20 percent from their peak.

Germany's DAX also fell to late 2016 lows, London's FTSE was down near April lows, and MSCI's world share index was just two points of a one-year low.

"This morning weaker stocks in Asia raised some eyebrows and overall sentiment is suffering from trade tensions, Italy to Brexit; a concoction of concerns," said ING strategist Benjamin Schroeder.

The euro also fell towards a two-month low and Italian bonds struggled before a European Commission meeting that could see Brussels take the unprecedented step of demanding changes to Italy's recently laid out budget plans.

Doubts about Britain's prime minister, mired in a stalemate over Brexit, kept the pressure on sterling.

All that contributed to the risk-averse mood, with the safe-haven Japanese yen and Swiss franc strengthening while higher-yielding currencies like the Australian and New Zealand dollars fell.

Markets were also waiting for Turkey's president to reveal his country's take on the killing of Saudi Arabian journalist Jamal Khashoggi at a Saudi consulate in Istanbul this month.

Saudi Arabia faces international pressure to provide all the facts about an incident that has raised a global storm and added the threat of sanctions against the kingdom to a list of market concerns.

President Donald Trump said on Monday he was not satisfied with what he had heard from Saudi Arabia about the killing, but expressed reluctance to punish the kingdom economically.

Investors worry that may lead to Saudi retaliation through crude oil, although a Saudi pledge to play a "responsible role" and keep markets supplied held down crude prices on Tuesday.