LONDON — Global shares tumbled for a sixth day on Thursday and oil prices slid to levels not seen since the early 2000s, after China guided the yuan lower and Shanghai shares tumbled by 7%, igniting fears of competitive devaluations across Asia.

Less than half an hour after the market opened, Chinese stock trading was suspended for a second time this week.

Brent crude prices skidded over 5% to an almost-12-year-low of $32.16, with worries over weaker demand from China adding to a persistent drag on prices caused by oversupply and near-record output levels.

European stock markets followed Asia lower, with the pan-European FTSEurofirst 300 index down 2.3% and the eurozone’s blue-chip Euro STOXX index falling 2.5%. MSCI’s 46-country All World index fell 1% to hit a three-month low, the sixth straight day of losses. The benchmark emerging stock index slid 2.5% to a six-and-a-half-year low as investors dumped risky assets.

"It’s looking pretty ugly," said ACIES Asset Management hedge fund manager and chief investment officer Andreas Clenow in Zurich. "We’ve been scaling down equity positions. It’s time to take a step back to re-evaluate the situation."

The People’s Bank of China (PBOC) set the yuan midpoint rate at 6.5646 per dollar, 0.5% weaker than the previous day’s fix. That was the biggest decline between daily fixings since August and the eighth day in row the PBOC had set a lower guidance rate.

Spot yuan fell to 6.5956 to the dollar, its weakest since February 2011. The offshore yuan rate hit a record low of 6.7600 to the dollar, before erasing its losses after suspected intervention by authorities.

Other regional currencies followed the yuan down as markets began to worry about competitive currency devaluations from trading partners. Singapore’s dollar hit a six-year low, the South Korean won touched a four-month low, and the Malaysian ringgit slumped to a three-month trough.

Investors fear China’s economy is even weaker than had been imagined, with Beijing, in a bid to help exporters, allowing the yuan’s depreciation to accelerate.

"The lower yuan fixing probably signifies greater risks to the Chinese economy than we know of, leading to risk-off trades," said CIBC World Markets head of currency strategy Jeremy Stretch.

Flight to safety

North Korea’s announcement on Wednesday that it had successfully conducted a test of a hydrogen nuclear device added to a growing list of geopolitical worries for investors.

"Geopolitical tensions stemming from Saudi-Iran tensions and North Korea’s nuclear test had already heightened the ‘risk off’ mood," said Monex Securities chief strategist Takashi Hiroki in Tokyo. "Resurfacing China risk was the extra psychological blow to the markets that led to the selloff in equities."

As investors fled to safety, the yen rose about 1% to 117.615 per dollar, its strongest in four-and-a-half years.

Top-rated German bonds, which are also considered a safe haven, benefited, too. Ten-year yields dropped below 0.50% for the first time in over a month.

Earlier, MSCI’s broadest index of Asia-Pacific shares outside Japan dropped 2% to its lowest since late September. Japan’s Nikkei shed 2.2%.

New rules Chinese authorities introduced this week that restrict selling by large shareholders did not go down well with investors and provided little tonic to jittery markets.

"This is crazy. Chinese regulators set off on this path in July and they cannot get out of it. They have ruined whatever hope investors still had in the market," said Mandarin Capital Partners founder Alberto Forchielli in Hong Kong.

Reuters