The U.S. services sector retrenched sharply in January to levels not seen since the 2001 recession, renewing fears about an economic slump, according to a survey released Tuesday.

The Institute for Supply Management's index of non-manufacturing plummeted to 41.9 from 54.4 in December, its largest monthly decline on record and a far greater drop than Wall Street expected. A Reuters poll of economists had produced a median expectation of a slip to 53.0.

"The recession has indeed arrived," said Jane Caron, chief economic strategist at Dwight Asset Management in Burlington, Vermont.