SEATTLE, United States — Amazon.com Inc on Tuesday began 48 hours of promotions as part of "Prime Day," a closely watched marketing event the company had postponed due to operational challenges from the coronavirus pandemic.

The event, typically held in July to boost summer sales, is now a kickoff to what will be an earlier holiday shopping season. The member-only discounts are a key way Amazon markets Prime, a fast-shipping and media-streaming service that incentivises subscribers to do more shopping on Amazon.

Rivals Walmart Inc and Target Corp are meanwhile hosting promotions at the same time. Online sales may prove critical for retailers as the pandemic forestalls the typical crowds at stores after the US Thanksgiving holiday.

At the pandemic's outset, Amazon was focused on shipping essential items to shoppers. Now its aim is to help customers with their holiday lists on Prime Day, said Jamil Ghani, a company vice president.

"It kicks off the holiday season," he told Reuters last month.

Amazon is bringing the event to Turkey and Brazil for the first time. In Latin America, Amazon has faced an uphill battle with local rivals.

A report by news site Reveal said the week around last year's Prime Day was the most dangerous for injuries at Amazon's fulfilment centres, prompting criticism by a prominent union.

"Amazon's Prime Day means more injuries and unacceptable levels of stress for its workforce," Stuart Appelbaum, president of the Retail, Wholesale and Department Store Union, said in a statement.

"During normal times it’s a gruelling period for workers. During a global pandemic it may well push workers beyond their limit," he said.

Amazon disputed the claims, saying employees' performance expectations and injury rates are not higher during the holiday season.

"The safety of our employees is our top priority," it said in a statement.

By Jeffrey Dastin; editor: Stephen Coates.