FARMINGDALE - Delivery services UPS and FedEx say late packages were expected to arrive starting Thursday and Friday.

The delivery services say the increased volume of seasonal online orders overwhelmed their systems and they had trouble keeping up. They also cited the aggressive ice storm in the Midwest as a problem for deliveries.

Extra UPS drivers were called in Wednesday night to try and compensate for the unexpected spike in deliveries.

Online retailer Amazon is refunding shipping costs and offering customers a $20 credit for the inconvenience.

Marshal Cohen, of the Port Washington-based NPD Group, says shippers underestimated consumers' last-minute online buying trends, which were fueled this year by companies offering free two-day shipping.