London (CNN) -- Britain's Royal Mail has added nearly 14,000 extra rounds for its postal deliverers, hoping to clear a huge holiday backlog caused by winter weather woes.
The service said it planned to complete 7,000 extra delivery routes Sunday, bringing packages, cards and letters to a million homes and addresses in an effort to catch up on deliveries during what it calls Britain's coldest December in decades.
About 6,500 extra deliveries were made last Sunday in the areas hardest hit by the severe weather, Royal Mail said.
"This is already the worst December weather the UK has seen for almost 30 years," Mark Higson, managing director of Royal Mail, said in a statement. "We are planning up 7,000 delivery rounds this Sunday as we continue our drive to deliver items as quickly as possible."
Online retailers are feeling the chill, too. Amazon.com's UK service has halted taking orders for its special rush delivery option and recommends giving e-gift cards instead of packages.
Retailer Marks & Spencer also said that it could no longer guarantee that orders placed now would arrive in time for Christmas, except for flowers.
Royal Mail had previously announced plans to add up to 3,000 extra workers and 250 delivery trucks to brave the icy roads.
It warned there's little time left to get packages delivered. Tuesday is the deadline for first-class mail and packets that customers want to arrive in time for Christmas, Royal Mail said.
CNN's Brian Walker contributed to this report