Los Angeles International Airport started off the year the way 2011 ended: passenger traffic was up but air cargo volume declined, airport officials announced Monday.

Total passenger traffic rose 5.4 percent in January, with 4.9 million passengers passing through the world’s sixth busiest airport. The biggest growth came from a 5.7 percent uptick in domestic passengers to 3.5 million, while international traffic rose 4.6 percent to 1.4 million, according to Los Angeles World Airports, the city agency that operates the facility.

However, total air cargo tonnage was down, falling more than 5 percent to 135,383. An 8.6 percent rise in air mail to 7,347 tons was offset by a nearly 6 percent drop in cargo freight to 128,037 tons.

The total number of landings and takeoffs, including passenger and cargo aircraft, rose 4 percent to 49,455.

Last year, LAX passenger traffic rose 4.7 percent, but total air cargo tonnage fell 3.8 percent, mostly because of a 4.2 percent drop in cargo freight.

Airport officials said last month they are unsure why cargo traffic is declining and planned to study the issue.