WASHINGTON — The number of Americans who applied for unemployment benefits fell by 4,000 last week to a seasonally adjusted 323,000, a five-year low. Layoffs have returned to prerecession levels.

The Labor Department said the less volatile four-week average fell 6,250 to 336,750. That’s the fewest since November 2007.

Net job gains averaged 208,000 a month from November through April, up from 138,000 a month in the previous six months.

Yet much of the job growth has come from fewer layoffs, not increased hiring. Overall hiring remains far below pre-recession levels, with unemployment at 7.5 percent.

The economy grew at an annual rate of 2.5 percent from January through March, a big improvement from the anemic 0.4 percent in the last three months of 2012.