A top White House adviser on Sunday warned that the U.S. is facing Great Depression-era economic pain from the COVID-19 pandemic as major business leaders said there is essentially no chance of a substantial economic rebound before the fall.

The grim forecasts were announced as governors across the country increasingly allow a limited number of businesses to reopen. They say sufficient public health safeguards are in place and they need to get the stunted economy moving again.

“Make no mistake: It’s a really grave situation,” White House senior adviser Kevin Hassett said on ABC’s “This Week.”

SEE ALSO: White House economic adviser: Not sure what McConnell was talking about on state bankruptcy

“This is the biggest negative shock that our economy, I think, has ever seen,” said Mr. Hassett, a former chairman of the White House Council of Economic Advisers under President Trump. “We’re going to be looking at an unemployment rate that approaches rates that we saw during the Great Depression.”

More than 26 million Americans have filed unemployment claims over the past five weeks. That number amounts to roughly one-sixth of the U.S. workforce. The peak unemployment rate during the Great Depression was approximately 25%.

Treasury Secretary Steven T. Mnuchin, meanwhile, said Americans should see a substantial rebound in July, August and September after the economy starts to reopen in May and June.

SEE ALSO: Steven Mnuchin: We’ll do whatever we need to do to win ‘war’

“We are putting in [an] unprecedented amount of fiscal relief into the economy. You’re seeing trillions of dollars that’s making its way into the economy, and I think this is going to have a significant impact,” Mr. Mnuchin said on “Fox News Sunday.”

Congress cleared a nearly $500 billion relief package Friday, and the Small Business Administration is slated to start accepting more applications for a popular small business lending program Monday morning.