HONG KONG — The battered Japanese stock market lurched into bear market territory Thursday, after a tumble of 6.4 percent took the combined decline in the Nikkei 225 index since a peak on May 23 to more than 21 percent.

A pronounced sell-off in the morning and early afternoon accelerated shortly before the markets closed in Tokyo. The Nikkei ended down more than 840 points at 12,445.38, its lowest level since early April.

Global markets reacted badly at first, with the Euro Stoxx 50, a benchmark for euro zone blue chips, down almost 2 percent in morning trading. But European shares later recovered most of their losses, and stocks on Wall Street opened quietly after new reports showed recent improvements in the American economy.

The drop in Japan on Thursday was one of many sharp declines seen in recent weeks, since a feverish six-month rally in Japanese stocks — incited by optimism over the government’s aggressive efforts to reinvigorate the listless economy — came to an abrupt end.

The Nikkei 225 soared more than 80 percent between mid-November and mid-May, but staged a sudden about-face with a 7.3 percent plunge on May 23.

Sentiment has been fragile and trading volatile ever since, as investors have taken stock of the challenges that face “Abenomics,” the economic policies of Prime Minister Shinzo Abe, and weighed the pros and cons of taking profits after the rally.

A renewed rise in the yen also has eroded a factor that, for months, had worked to support Japanese stocks. The yen weakened substantially between November and May – a welcome development for Japanese exporters as it made their goods less expensive for customers overseas.

But the currency’s move, like that of the stock market, reversed in late May. On Thursday, the yen traded around 94.00 to the American dollar, its strongest level since early April.

In Tokyo, Yoshihide Suga, the chief cabinet secretary, brushed off the market plunge.

“I feel it’s important not to swing from joy to sorrow every time stock prices rise or fall, and keep on doing what we need to do,” Mr. Suga said at a news conference Thursday morning, as shares fell. “The Japanese economy is steadily improving.’’

The Bank of Japan governor, Haruhiko Kuroda, met with Mr. Abe on Thursday to exchange views on the economy, according to local news reports. Mr. Abe told the governor he was determined to do his part in putting a growth plan into action, Mr. Kuroda later told reporters. Mr. Kuroda told the prime minister that the central bank was committed to supporting the Japanese economy through monetary stimulus.

Mr. Kuroda also said he expected markets to soon “calm down to reflect positive developments in the economy,” according to the Nikkei Web site. On Monday, the Japanese government revised its first-quarter gross domestic product figures, saying its economy grew at an annualized pace of 4.1 percent between January and March, better than the 3.5 percent it initially reported. But that upgrade has not been enough to calm investor jitters.

Factors beyond Japan also have helped send markets lower around the world.

In China, which is a key engine of global growth, the flow of economic data in recent weeks has reinforced the picture of an economy that is struggling to regain momentum.

And in the United States, comments on May 22 by Ben S. Bernanke, the chairman of the Federal Reserve, that he and his colleagues might consider paring back their bond-buying programs “in the next few meetings” if the economy shows signs of improvement have helped fan global nervousness. Investors and analysts have struggled to assess the implications of even a small withdrawal of the bond buying that has supported markets in recent years.

In the United States, the Dow Jones industrial average and the Standard Poor’s 500-stock index have sagged 3.2 percent and 4 percent, respectively, in the past three weeks. The DAX in Germany has fallen about 4.5 percent and the CAC 40 in France has dropped more than 6 percent.

Key markets in the Asia-Pacific region have tumbled even more. The Straits Times index in Singapore and the S.P./ASX 200 in Australia have lost more than 9 percent since May 22, and in Hong Kong, the Hang Seng has shed more than 10 percent.

A pessimistic outlook issued Wednesday by the World Bank added to the gloom, with Kaushik Basu, the bank’s chief economist, noting in a news release that “the slowdown in the real economy is turning out to be unusually protracted.”

The bank, based in Washington, cut its forecast for global growth to 2.2 percent from a January forecast of 2.4 percent growth.

In explaining the revision, Mr. Basu cited high unemployment in the developed world and slower-than-expected growth in emerging economies. He also noted that India was expanding at a rate below 6 percent for the first time in a decade.

Hiroko Tabuchi contributed from Tokyo and David Jolly contributed from Paris.

Article source: http://www.nytimes.com/2013/06/14/business/global/asian-stock-markets.html?partner=rss&emc=rss