Nonfarm payrolls fell 80,000 in March, the Labor Department said Friday, its biggest decline in five years, after falling by 76,000 in both January and February. Both were revised to show even bigger losses.

Had it not been for a rise in government jobs last month, payrolls would have fallen by around 100,000.

The unemployment rate, which is calculated using a separate survey of households, jumped 0.3 percentage point to 5.1%, the highest since September 2005, when it was also 5.1%.

“This report is telling us that the recession started awhile back, in December,” said Nigel Gault, the chief United States economist at Global Insight, a research firm. “It is not like we are starting this month. We’re in it; we’ve been in it.”

John Ryding, chief US economist at Bear Stearns, said: “This magnitude of a rise in the unemployment rate has never occurred in the postwar period without the economy being in recession.”

But the size of the job losses was not large by the standards of past recessions and, surprisingly, hours worked moved up.

Michael Feroli, an economist at JPMorgan, said it was consistent with a “mild start to a recession”.

US companies did not add as many workers during the previous upswing as they did in past cycles, suggesting that they may not be as quick to shed workers during the downturn.

“Today’s jump in unemployment to 5.1 per cent may well be a harbinger of things to come,” said Michael Woolfolk, senior currency strategist at the Bank of New York Mellon.

March job losses were concentrated in the construction (–51,000), manufacturing (–48,000) and employment services (–41,800) sectors.

A succession of job losses could force the US economy into a more serious downturn as consumers cut back on spending, sapping economic growth.

Wage increases continue to fall behind inflation, meaning many employees are actually earning less than a year earlier. Average hourly salaries ticked up 5 cents, or 0.3 percent, in March, and were running 3.6 percent higher than a year earlier. But consumer prices rose 4 percent over the same period.

Average hourly earnings increased $0.05, or 0.3%, to $17.86. That was up just 3.6% from a year earlier, suggesting wage costs remain under wraps. Fed officials are counting on the slack that comes from a slowing economy to offset higher energy, food and commodity prices and the weak dollar and keep inflation in check.

Mr. Bernanke on Wednesday warned for the first time that "a recession is possible." Yet last month's payroll decline won't come as too much of a surprise, as Mr. Bernanke also told lawmakers Wednesday that "much necessary economic and financial adjustment has already taken place, and monetary and fiscal policies are in train that should support a return to growth in the second half of this year and next year."

Still, the jobs slump may heighten fears at the Fed of a negative "feedback loop" in which financial market strains lead to a weaker economy, which in turn leads to more financial turbulence.