LOUISVILLE, Kentucky (AP) — Mellany Sorrell's face glistened with sweat as she lifted packages and seemed in constant motion during the holiday rush at the epicenter of UPS' global air shipping network.

The 29-year-old methodically hoisted boxes and put them gingerly onto a conveyor belt — keeping them on a synchronised journey that could end under countless Christmas trees. After emptying a hulking container so big that she could step inside it, Sorrell caught her breath before starting again with another container stuffed with boxes. Each container holds up to six tons of cargo.

The holiday shipping rush is expected to peak for UPS today, when the world's largest shipping carrier projects it will deliver about 22 million small packages. For the entire holiday season, UPS plans to deliver roughly 400 million packages worldwide, up slightly from the 2008 holiday season.

There is no syrupy Christmas music blaring inside the massive UPS Worldport hub in Louisville, Kentucky, only the roar of conveyor belts. Still, workers say they get caught up in the holiday spirit.

"You're making millions of people's Christmases come true," said Matthew Deeds, a supervisor.

Co-worker John Pidwell added: "We're basically playing Santa Claus."

UPS, based in Atlanta, hired about 50,000 seasonal workers to keep pace with the extra volume this holiday season, including about 700 extra staff at Worldport. The Louisville facility employs about 10,000 people and sorts up to 350,000 packages hourly. On average, about 1.2 million packages pass through every day. Volume reaches 2.5 million packages at the holiday peak. UPS has other domestic air hubs in Philadelphia, Dallas, Hartford, Connecticut, Ontario, California, Rockford, Illinois, and Columbia, South Carolina, plus a network of international hubs.

Worldport was a beehive of activity during a recent overnight shift — when UPS sorts and ships most of its packages for next-day delivery. Cargo jets took off and landed, and the smell of aviation fuel wafted through the December chill. Pint-sized tractors, called tugs, hauled huge package containers from the planes and later reloaded them after the sorting was done. The company's active fleet of 211 aircraft includes Airbus A300s, Boeing 757s, 767s, 747-400s and MD-11s.