A record 6.6 million Americans applied for unemployment benefits last week as the new coronavirus struck the U.S. economy and sent a recently booming labor market into free fall.

The large number of claims was double the 3.3 million who sought benefits two weeks ago as the U.S. shut down parts of the economy in an effort to contain the virus. Jobless claims, a proxy for layoffs, provide temporary financial assistance for workers who lose their jobs.

About 6% of the U.S. labor force has filed for jobless benefits in the last two weeks, up from 0.3% at the end of February, showing the toll from the coronavirus is gripping an ever-larger share of the U.S. economy. States indicated people from an array of industries—including restaurants, retail, trade and construction—sought unemployment benefits last week.

“The speed and magnitude of the labor market’s decline is unprecedented,” said Constance Hunter, chief economist at KPMG LLP. Ms. Hunter said she expected that millions more claims will be filed in the coming weeks and projects 20 million jobs will be lost. “We didn’t see this in the global financial crisis. We didn’t see this in the Great Depression. There’s been a total decimation of consumption.”

The Congressional Budget Office on Thursday updated economic projections based on the jobless-claims data and recently enacted stimulus measures. It expects U.S. unemployment to exceed 10% in the second quarter and gross domestic product to fall by more than 7%, or an annualized 28%. “Those declines could be much larger, however,” the CBO said, adding that its estimates are “highly uncertain at this time.”