NEW YORK — FedEx plans to run Christmas Day deliveries in some markets to help complete shipments after severe weather interrupted services in the run-up to the holiday.

“FedEx is operating with slight delays this morning, but we are continuing to make adjustments and do everything we can to minimize impact on our customers,” according to an e-mailed statement on Thursday. The company didn’t identify where the slowdowns were occurring.

FedEx’s efforts reflect the increasing importance of online orders as a source of Christmas gifts – and the extreme time-sensitivity of those shipments. In 2013, a last-minute surge of holiday orders converged with winter weather to leave United Parcel Service Inc. unable to deliver some packages in time, triggering an avalanche of complaints on social media.

The National Retail Federation has forecast a 3.7 percent increase in holiday spending this year, and merchants rolled out discounts – including on shipping costs – early to grab their share. This year, 90 percent of all retailers are providing free delivery for online purchases, up from 78 percent in 2014, according to HRC Advisory.

Customer counters at FedEx Express stations across the country will be open from 9 a.m. to 1 p.m. on Friday so customers can pick up shipments, the company said. Weather began interrupting operations on Wednesday, FedEx said. “We made operational adjustments to keep our team members safe and to avoid major service disruptions,” the company said.

UPS, which refined its strategy this year for peak-season operations, has been delivering on-time at about a 98 percent rate this week, said Dan Cardillo, a spokesman. While the company doesn’t typically operate on Christmas, it is monitoring volume and could ask “a small fraction” of workers to sort packages or deliver on Friday, he said by email.

“Everything was processed overnight and we expect to maintain current on-time performance,” Cardillo said.

“We will be working into the evening tonight to get everything to customers.”