The US trade deficit in February fell sharply to its lowest level since 2009, likely as a labour dispute at one of the country's main ports depressed both imports and exports.

But the smaller deficit, which could see economists raise their first-quarter growth estimates, is probably temporary given a stronger dollar and weaker global demand.

The US Commerce Department said the trade deficit narrowed 16.9% to $35.4bn, the smallest since October 2009.

January's shortfall on the trade balance was revised to $42.7bn from a previously reported $41.8bn.

Economists polled by Reuters had forecast the trade deficit slipping to $41.2bn.

When adjusted for inflation, the deficit narrowed to $50.8bn in February from $54.6bn the prior month.

The now-settled labour dispute at the West Coast ports appears to have slowed the flow of imports and exports. 

The strong dollar, weak global demand as well as lower crude oil prices also likely impacted the trade balance in February.

While the smaller trade deficit is positive for gross domestic product, it does little to change views that economic growth slowed sharply in the first quarter.

Growth estimates range between a 0.6% and 1.7% annual pace. The economy grew at a 2.2% pace in the fourth quarter.

In February, imports tumbled 4.4% to $221.7bn, the lowest since April 2011. Imports of petroleum products were the lowest since September 2004.

Exports fell 1.6% to $186.2bn in February, the smallest since October 2012.

Exports to Canada and Mexico - the main US trading partners - fell in February. Exports to China tumbled 8.9%, while those to the European Union were unchanged.

Imports from China plunged 18.1%, pushing the politically sensitive US-China trade deficit down 21.2% to $22.5bn.