MEMPHIS, Tennessee: Federal Express has warned that rising numbers of COVID-19 cases caused by the Omicron variant will lead to staff shortages and delays to shipments transported by air.

"The explosive surge of the COVID-19 Omicron variant has caused a temporary shortage of available crew members and operational staff," the company said in a statement.

Severe winter storms in the U.S., including one that hit the main FedEX air hub in Memphis, Tennessee, have caused challenges, and FedEx officials said they are implementing contingency plans and adjusting operations to minimize disruptions, the company added.

Rival United Parcel Service (UPS) said employees calling in sick due to Omicron are not impacting their services, as it also has contingency plans in place.

"Recent weather events in the Louisville, Kentucky and Philadelphia, Pennsylvania areas caused some delivery delays," said a UPS spokesperson, as reported by Reuters.

The rapid spread of the Omicron variant and extreme winter weather have forced several American airlines to cancel flights, as pilots and crew were required to quarantine.

On January 6, inadequate staffing levels and other issues forced the U.S. Postal Service, one of the country's largest public employers, with 650,000 employees, to request a delay in carrying out the Biden administration's new vaccine or testing requirements covering large businesses.

According to Reuters, U.S. coronavirus deaths have risen by 2,133 to reach 836,901.