WASHINGTON (AFP) - The US economy grew at an annual rate of 2.4 per cent in the first quarter, according to the Commerce Department's official second estimate of growth released on Thursday.

The tenth-point dip from the first estimate of 2.5 per cent was unexpected by most analysts, who forecast the rate would remain unchanged.

Still, gross domestic product growth in the first quarter was the strongest since the fourth quarter of 2011, and far stronger than the 0.4 per cent pace in the final quarter of 2013.

The downward revision was due partly to lowered estimates of exports and government spending, while consumer spending was revised higher.

"The general picture of overall economic activity is not greatly changed," the Commerce Department said.