With the holidays fast approaching, the U.S. Postal Service has entered its busiest week of the year. Workers at USPS's massive processing and distribution center on Lindbergh Boulevard in Southwest Philadelphia are feeling the rush.

Employees are putting in long hours to keep up with the surge. According to USPS, the Southwest Philadelphia facility is now handling 6.5 million letters every day, which is about a 25% jump compared to a normal day.

"I guess we're like Santa Claus for the Post Office, where we get the mail and the packages delivered to the people," USPS distribution clerk Detra Kemp said.

To keep mail moving, USPS is relying heavily on automation. Machines inside the facility can scan and sort packages by ZIP code up to five times faster than a human, helping workers stay ahead of the holiday spike.

"It's just moving the mail to where it needs to go and more the expeditiously," USPS mail handler Andrew Little said.

Despite the fast pace, employees said morale stays high. Carolers stopped by Thursday afternoon to sing and lift spirits as staff worked around the clock.

"The mood here around the holidays is everybody energetic, ready to push the mail to get the mail out to the people," USPS mail handler Malik Johnson said.

USPS officials are urging customers to take extra care when sending packages. Missing apartment numbers, incomplete addresses and incorrect ZIP codes remain some of the biggest causes of delays.

"We like to make sure that the packages are packed properly," USPS spokesperson Paul Smith said. "A lot of people make some mistakes."

The USPS expects the holiday rush to remain strong through Dec. 31, as Americans continue shipping gifts, cards and year-end mail.