Consumer prices fell in the eurozone for the first time since 2009, according to official data released on Wednesday, putting further pressure on the European Central Bank to act to prevent a downward price spiral that could further damage the fragile banking sector and undermine growth for years to come, reports The New York Times..

Consumer prices in the eurozone contracted by 0.2 percent in December compared with a year earlier, according to a preliminary report from Eurostat, the European Union’s statistics agency. Even before the recent collapse in oil prices, inflation in the region had been falling amid slack spending by consumers and businesses that makes it difficult for companies to raise prices.

A separate report from Eurostat showed that the eurozone jobless rate was unchanged at 11.5 percent in November. For the 28-nation European Union, the unemployment rate was 10 percent, down from 10.1 percent in October.

Taken together with recent statements by Mario Draghi, the president of the European Central Bank, the latest inflation data will further heighten expectations that the central bank will announce aggressive measures when it meets in Frankfurt on Jan. 22. Analysts expect the central bank to say it is ready to begin effectively printing money that it would use to buy eurozone government bonds.

The reports reinforce the impression that Europe’s economy could be heading back toward recession, as the pace of growth is insufficient to restore the moribund labor market or create inflationary pressure. The eurozone economy expanded just 0.6 percent in the third quarter on an annualized basis, and recent data suggests that the pace has slowed in recent months.

Consumer prices in the eurozone had not contracted on an annual basis since October 2009, as the global financial crisis was ebbing. The December rate was down from a 0.3 percent increase in November, already far below the European Central Bank’s target of holding inflation close to, but below, 2 percent.

Analysts had expected consumer prices in the eurozone to decline 0.1 percent, the same rate posted by Germany on Monday. They had expected the eurozone jobless rate to come in at 11.5 percent.

Unemployment in the eurozone, which expanded to 19 members this month with the entry of Lithuania, peaked at 12 percent in 2013. The dismal labor market has weighed on consumer spending.

Economists fear that unemployment could rise again if the eurozone succumbs to deflation. When deflation takes root, consumers tend to delay purchases because they expect prices to fall further. Corporate profits sag, and companies are forced to fire workers. Deflation also raises the cost of servicing loans in real terms, putting stress on borrowers and pressure on their lenders.

Deflation is considered even more dangerous than runaway inflation because it is very difficult to reverse. Japan’s experience in the 1990s showed that traditional monetary instruments are largely ineffective with nominal interest rates at zero.

A single month of falling prices does not meet the classical definition of deflation as a widespread, self-sustaining decline in prices. But well before consumer prices tipped below zero, the eurozone’s very weak inflationary pressures had raised alarms among economists, who feared that policy makers were underestimating the threat.

International Monetary Fund economists warned early last year that the difference between ultralow inflation, which they called “lowflation,” and outright deflation was mainly a matter of degree, as the weak price pressures could “scupper the nascent recovery and pressure the most fragile countries.” Deflation would be particularly painful for eurozone members like Spain and Greece, which would be hobbled in their efforts to increase competitiveness relative to Germany.

The so-called core rate of inflation, which excludes volatile energy and food costs, rose 0.8 percent. The price of Brent crude, the European benchmark, touched below $50 on Wednesday for the first time since 2009 amid a continuing rout in the oil market. Falling fuel prices are a boon to consumers, providing a demand stimulus to an economy that economists expect to grow only a little more than 1 percent this year.

Mr. Draghi, the central bank president, said last week that the risk of deflation “cannot be ruled out completely, but it is limited.” But he added, “If inflation remains low for a long time, people might expect prices to fall even further and postpone their spending.”

“We are not there yet,” Mr. Draghi said in an interview with the German newspaper Handelsblatt. “But we need to tackle this risk.”

Many economists expect the central bank to undertake an unconventional policy similar to the so-called quantitative easing used by the Federal Reserve to stimulate the American economy after official interest rates were already effectively at zero. But quantitative easing is a divisive issue in Europe because of questions about how the European Central Bank would allocate bond buying among the 19 countries of the eurozone, and who would pay if a government defaulted on bonds held by the central bank.

Some analysts expect the central bank to wait until March to start a bond-buying program, to allow more time to work out these problems.

Expectations that the Federal Reserve will move this year toward reining in ultralow interest rates in the United States even as the European Central Bank prints more money have helped push the euro to its lowest levels against the dollar in years.

Investors have also been snapping up government bonds of eurozone countries amid expectations that European Central Bank action will make them more valuable. Yields on German, French and Belgian bonds have all hit record lows this week.