— The prospect of a double-dip global recession hit Asian and European markets on Friday, driving Tokyo’s key stock index to its lowest point in five months and deepening concerns for Japan’s already-feeble economy.

The Nikkei 225 — reacting to Wall Street’s worst day since the 2008 financial crisis — was down 3.72 percent Friday, closing at 9299.88. Hong Kong’s Hang Seng index sank 5.13 percent; other benchmarks in South Korea, Taiwan and Australia fell between 3.5 and 5 percent, as investors came to grips with a crisis that policymaking might do little to slow.

European markets also weathered more sharp dives in early trading Friday, with key indexes in London and Frankfurt diving more than 2 percent. More worrisome, investors continued to dump the bonds of troubled Italy and Spain, sending the borrowing costs for those nations to new 14-year highs. Yields on Italian bonds jumped to 6.35 percent, almost matching Spain’s 6.358. Both countries are approaching the 7 percent threshold that forced the smaller economies of Greece, Ireland and Portugal to launch bailout talks.

Yet analysts fear that Spain and, especially, Italy may be too big to bail out, with the amount needed to prop them up dwarfing the current rescue fund established by European leaders to fend off crises.

That has effectively left one battle plan for the Europeans: intervention by the European Central Bank. On Thursday, the ECB acted to bring down the prices of European bonds, buying up millions in Portuguese and Irish debt. But it had not yet begun the task of buying up Spanish and Italian bonds, which would require purchases on a far larger scale.

The decision to restart the buy-back program, dormant for months, came over the objections of Germany’s Bundesbank.

“The decision to resume the [bond purchases] was unexpected by many, including ourselves, but we reckon it was a quite half-hearted decision, as the ECB seems to have focused only on Portuguese and Irish bonds and for limited amounts,” Giada Giani, an economist at Citibank, wrote in a report. “This suggests the hurdle for the ECB to intervene on the Italian and Spanish bond markets remains extremely high for two main reasons, we think.

“First, the ECB seems to think Italy and Spain have not done enough to put their houses in order,” she continued. “Second, and probably more important, the resources required to support Italy and Spain would have to be much bigger than those used for Portugal, Ireland and Greece combined in the past 15 months.”

Though global financial concerns stem mostly from the U.S. and Europe, Asian investors also are worried about the course that could be set for weeks to come by Friday’s looming U.S. jobs report.

In Tokyo, economists drew a comparison to Japan’s experiences in the previous two decades, where central bank policies and fiscal stimulus failed to re-power a shrinking economy, and where companies cut spending at the same time that the government tried to cut debt.

“The U.S. is going through exactly the same process — exactly the same confusion and debate — that Japan went through 15 years ago,” said Richard Koo, the Tokyo-based chief economist at the Nomura Research Institute. “This is what happened in 1997 here: The government tried to reduce debt when the private sector was deleveraging.”

Friday, bonds gained and commodities dropped as traders looked for safe investments. Despite its massive debt, investors still see Japan’s yen as a safe choice, creating upward pressure on the yen at the same time that Japanese authorities are trying to weaken their own currency.

One day after Japan’s finance ministry intervened in the currency market, weakening the yen and driving it away from record-high levels, the yen on Friday again appreciated slightly. It strengthened Friday some 0.9 percent, standing at 78.47 against the dollar by the early evening. A day earlier, the yen was briefly trading at 80.05 against the dollar — a level more favorable to Japan’s export-dependent corporations, which need a weak yen to make their products affordable overseas.

Japan’s economics minister, Kaoru Yosano, said Friday that Japan wouldn’t be afraid to intervene again in the market, saying, “It’s too hasty to think Thursday’s intervention was a one-off measure.”

The Nikkei took its sharp tumble in the first 10 or 15 minutes of trading Friday, falling from 9469.16 to 9264.09. It then recovered slightly and held steady for the rest of the day.

The index hit its lowest point since March 18 — a point when Japan was reeling from a 9.0-magnitude earthquake, a massive tsunami and a series of meltdowns at a coastal nuclear plant.

The broader Topix index on Friday also took a hit, with all of its 33 sectors losing ground, including oil and trading houses.

Faiola reported from London.