United Parcel Service and FedEx Corp. scrambled to deliver holiday gifts after Christmas Day following an unexpected surge in online ordering that brought delays and plenty of customer complaints.

The nation's largest package-delivery fleets struggled to respond to huge volume increases from late-ordering customers. Online orders jumped 37% during the last shopping weekend before Christmas compared to a year ago, according to IBM Digital Analytics.

FedEx set record volumes each Monday in December, including handling more than 22 million packages on Dec. 23, an 11% increase from the year earlier, a company spokesman tells Automotive Fleet.

"We continue to operate normally," Parul Bajaj said Friday. "Every single package is important to us, and we will continue to work directly with customers to address any isolated incidents."

Packages arriving for delivery at UPS shipping centers exceeded the 7.75 million it expected to enter its air network on Monday, a spokesperson told the Wall Street Journal. UPS handles 45% of the package deliveries in the U.S.

"The volume of air packages in the UPS system did exceed capacity as demand was much greater than our forecast," according to a company statement Thursday. By Friday, UPS continued to "get packages to their destination as quickly as possible."

To handle the delivery crush, UPS and FedEx called in extra drivers and reportedly rented U-Haul trucks in several areas of the country to deliver packages, reported CBS News.

Delivery delays were reported in various states, including Alabama, California, Georgia, Kansas, Louisiana, Nevada, Ohio, Oklahoma, South Carolina, Texas and Virginia, reports the Associated Press.

By Paul Clinton